InsideCover_Plant Breeding in Scandinavia

PREFACE

The material presented in this book is the result of a special enquiry made by the writer into the present status of plant-breeding in that part of Northern Europe known as Scandinavia, which comprises the three countries of Sweden, Norway and Denmark. For various reasons practically all the time available for this investigation (about nine months) was spent at the headquarters of the famous Plant Breeding Institution known as the “Swedish Seed Association” situated at Svalöf, a little village in the southern part of Sweden. My remarks will therefore concern very largely the work of this institution, although reference will be made from time to time to endeavors of a similar nature elsewhere.

The main object of this publication is to give a general survey of the work conducted at Svalöf from the time of its inception and to indicate some of the facts and circumstances which have led to the adoption of principles of breeding now recognized at that place. For this exposition I claim neither originality nor completeness. The facts submitted have been taken from printed or private records to which reference is made in practically all cases.  The one object has been, in the words of Huxley, “to know what is true in order to do what is right.”

I am also deeply sensible of the great obligation I am under to Prof. Hjalmar Nilsson, director of the Institution at Svalöf, not only for permission to investigate the work, but still more for the personal assistance and great courtesy which he at all times extended. In no less degree am I indebted to Drs. Nilsson-Ehle, Hans Tedin, Hernfrid Witte and Mr. Lundberg who, as experts in direct charge of their respective branches, were most untiring in their efforts to present their work exactly as it is.

While efforts have been made to render the following pages as intelligible to the general public as the nature of the subject would permit, they are addressed primarily to the scientific reader.

In order more fully to appreciate the difficulties as well as the possibilities associated with the production of more useful forms of cultivated plants in Sweden, the reader is commended to study carefully the Appendix in which are considered the geographical position, physiography, climate, precipitation etc., of this country.

The scientific aspects of the achievements in Sweden are of special interest by reason of the extent to which they add to our knowledge of biological problems.

L. H. NEWMAN,

Ottawa, Canada, June 15, 1912.


CONTENTS

PAGE
I.―INTRODUCTION
      13
   Present position of the Swedish experts re principles of plant improvement (summary)      15
II.—THE SWEDISH SEED ASSOCIATION (General résumé)
   Aim of the Association      15
   Circumstances leading up to its organization      15
      Early Swedish Agriculture      16
      Experiences of Schübeler      16
   Membership      17
   Administration      17
   Branch Station      18
   Funds      18
   Experimental Grounds      18
III.—THE SYSTEM OF PLANT IMPROVEMENT AT SVALÖF AND ITS DEVELOPMENT.—
   The method first employed
      18
      Early laboratory studies      19
      Fnial valuation of sorts      21
      RESULTS FROM CONTINUOUS MASS-SELECTION      21
   Introduction of the Pedigree System of Selection at Svalöf
      25
      "Form separation” on the basis of correlations      27
      Classification of forms into groups      27
      System of numbering sorts      27
      Absence of hereditary variations in pedigree cultures      28
      Theory of unit characters      28
      Johannsen’s pure line theory      28
      Early ideas of artificial hybridization      30
      Specialization of the work      31
      CORRELATION OR THE ASSOCIATION OF CHARACTERS      31
      Origin of Primus barley      36
      Dangers associated with mass-selection      39
      Stooling in grain vrs. yield and quality      39
      The system of exclusive ‘form separation’ abandoned      42
IV.—THE COMPOSITION OF A RACE OF CEREALS AND ITS VARIABILITY.—
   Biotypes and Elementary species      43
   Multiformity: of Probstier oats      43
   Independent nature of different characters      47
   Natural crossing in cereal grains      48
   Individual and partial modifications within pure lines      49
   Influence of mass-selection      50
   THE ORIGIN OF ‘ABERRANT FORMS’ AS QUANTITATIVE HEREDITARY VARTATIONS      50
   Mendel’s Law of Hybrids      51
   The theory of Presence and Absence      57
   The theory that certain characters may possess more than one unit, each of which has the same external effect      60
   Crossing between sorts which are apparently identical in regard to certain characters      61
   Crossings between sorts which differ in regard to certain characters      64
   THE ORIGIN OF ‘ABERRANT FORMS’ AS ‘MUTATIONS’      70
   THE NATURE AND CLASSES OF VARIATION (SUMMARY)      72
   AN EXPLANATION OF THE OCCURRENCE OF CERTAIN ABERRANT FORMS UNDER DOMESTICATION      74
      Kotte(cone) wheat      74
      Reappearance of dominant heterozygotes in field cultures      74
V.—PRACTICAL APPLICATION OF PRINCIPLES NOW RECOGNIZED IN CEREAL BREEDING AT SVALOF
   Line Breeding      76
   Artificial hybridization      78
   The necessity of systematic crossing work      79
   Two categories into which crossing work at Svalöf falls      81
      Repeated crossings      81
      Obtaining constancy in new combinations      81
      Creating of plant populations      82
   Mass selection      83
   PRACTICAL IMPORTANCE OF SORT PURITY—      86
      Definition of a "Sort"      86
VI.—METHODS OF WORK IN CEREAL BREEDING AT SVALOF.
   Size and arrangement of plots      87
   Pedigree cultures      87
      Head-to-the-row method      89
   Preliminary trial plots      90
   Large comparative trial plots      93
   Importance of a proper interpretation of results      95
   Method of handling artificial crossing products      97
   Local trials and Branch Stations    100
   Local breeding    102
   Multiplication of sorts intended for distribution    103
   Measures taken to maintain purity of seed stocks    103
   Book-keeping    103
   Grading rust and smut    104
   Grading strength of straw    104
   Laboratory Work    105
VII.—SUMMARY OF WORK DONE WITH DIFFERENT CROPS AND RESULTS OBTAINED,—
    
   1.   The Breeding of Autumn wheat in Sweden    106
          Leading sorts in Middle Sweden    109
          Leading sorts in Southern Sweden    111
          Table of yields of leading sorts at Svalöf    114
          Pedigree plots under investigation in 1910    114
   2.   Spring wheat breeding    117
   3.   Oat breeding    119
          Quality in oats    120
          Leading White Oat sorts    122
          Leading Black Oat sorts    124
          Early sorts for the far North    126
          Pedigree plots of oats under investigation in 1910    127
          Summary of present work in oat breeding    129
          Tables of yields    129
   4.  Barley breeding    130
          Different sorts produced for different conditions    131
          An ideal brewing barley    132
          Classification of barley types    133
          Handling of brewing barley    137
          Six-rowed barley    141
          Leading two-rowed sorts    141
          Table of yields of two-rowed sorts at Svalöf    143
          Two-rowed sorts including pedigree pluts under investigation in 1910    143
   5.  Breeding of Pease    146
          System of classification    148
          Table of yields of leading sorts    149
          Description of leading sorts    151
          Pedigree plots under investigation in 1910    152
   6.  Breeding of Clovers and Grasses    152
          Principles and methods in the improvement of Red Clover    154
          Multiplication of superior types    155
          Principles and methods in the breeding of grasses    155
          Results obtained with grasses    166
          Local trials    167
          Summary of work with grasses and clovers    167
   7.  Potato Breeding    168
          Principles of improvement in potato breeding    168
          Production of sorts from the true “seed”    170
          Starch determination    173
          Field trials    176
          Local sort trials    177
          Degeneration in potatoes    178
          Table of yields and of starch content of leading sorts at Svalöf    180
          Cooking qualities    181
VIII.― APPENDIX
    183
IX—LITERATURE CITED
    188

LIST OF ILLUSTRATIONS

(Photographs, Diagrams and Tables)

____________
             PAGE
FIG.  I.—Main Building, Swedish Seed Association, Svalöf.   Frontispiece
FIG.  II.―Two mass-selected barley sorts                  22
FIG.  III.―Pedigree of Clay and Moss Barleys                  23
FIG.  IV.―Svalöf’s Selected (Renodlad) Squarehead wheat                  26
FIG.  V. & VI.―Types of panicles in Oats             32-33
FIG.  VII.―Different classes of Spikelets                  34
FIG.  VIII.―Frequency curve of variation in weight of kernels from different pure cultures                  47
FIG.  IX.―Graphic explanation of the Law of Mendel                  53
FIG.  X.―Club-wheat (T. Compactum)                  66
FIG.  XI.―Second generation (F2) from the wheat crossing Club X Pudel                  66
FIG.  XII.―Svalöf’s Pudel wheat                  66
FIG.  XIII.―"False Wild oats"                  71
FIG.  XIV.―Removing impurities by hand from large culture of Elite Stock Seed grown at Svalöf                  85
FIG.  XV.―Scheme showing general plan of procedure recommended at Svalöf in ordinary line-breeding work                  88
FIG.  XVI.―A large comparative trial plot separated from its neighbor by Spring rye                  89
FIG.  XVII.―Sowing pedigree plots of wheat and rye at Svalöf                  90
FIG.  XVIII.―Preliminary trial plots of Autumn wheat                  91
FIG.  XIX.―Dr. Nilsson-Ehle taking notes on preliminary trial plots                  92
FIG.  XX.―Sowing large comparative trial plots                  94
FIG.  XXI.―Harvesting pedigree plots                  97
FIG.  XXII.―View of experimental plots of Spring grains in 1910                100
FIG.  XXIII.―Method of grading strength of straw                105
FIG.  XXIV.―Prof. Hjalmar Nilsson selecting oat plants for photographing                105
FIG.  XXV.―Plot of Selected Squarehead wheat adjoining a pedigree out of the same                107
FIG.  XXVI.―Dr. Nilsson-Ehle taking notes on the most promising plot (5th generation) from the crossing Pudel X Swedish Velvet Chaff                110
FIG.  XXVII.―Dr. Nilsson-Ehle examining segregation in the Club X Pudel wheat crossing                111
FIG.  XXVIII.―Table of yields of hardy autumn wheat sorts tested at Ultuna; 1904-1909.                111
FIG.  XXIX.―Extra Squarehead II. wheat                112
FIG.  XXX.―Table of yields of leading autumn wheat sorts at Svalöf, 1890-1909.                114
FIG.  XXXI.―Spring wheat cultures Nos. 102, 103 and 104 from the crossing 0201 X Pearl                118
FIG.  XXXII.―Diagram showing per cent hull in oats tested at Svalöf and Luleå in 1904                120
FIG.  XXXIII.―Oat plots—Gold Rain (No.19) and Svalöf’s Dala,0924 (No. 20)—showing relative strengths of straw                124
FIG.  XXXIV.―Table of yields of White Oats at Svalöf, 1900-1909                129
FIG.  XXXV.―Table of yields of Black Oats at Ultuna, 1897-1909                130
FIG.  XXXVI.―Classification of Barley types                133
FIG.  XXXVII & XXXVIII.―Distinguishing characters in Barley kernels         135-136
FIG.  XXXIX.―Dr. Tedin examining botanical marks on a kernel of barley to decide type to which it belongs                137
FIG.  XL.―Dr. Tedin taking final notes re date of ripening, etc., on large barley plots                139
FIG.  XLI.―Dr. Tedin collecting types of barley for photographing                140
FIG.  XLII.―Table of yields of leading two-rowed barley sorts at Svalöf                143
FIG.  XLIII.―Dr. Tedin crossing Pease                147
FIG.  XLIV.―Table of yields of Pease at Svalöf, 1893-1909                149
FIG.  XLV.―Svalöfs Solo Pease                150
FIG.  XLVI.―Comparison of Swedish and foreign Red Clover sorts                153
FIG.  XLVII.―Orchard Grass: Average panicles of mother plant (M) and of a number of its progeny                156
FIG.  XLVIII.―Timothy cultures at Svalöf showing a dwarf race                158
FIG.  XLIX.―Timothy spikes from different biotypes                159
FIG.  L.―Orchard Grass: Average panicles from different biotypes                160
FIG.  LI.―Diagram showing method of grass breeding practiced                163
FIG.  LII.―View from tower of Main Building, Svalöf, showing pedigree grass plots                164
FIG.  LIII.―Sowing Orchard Grass multiplication plot in drills                165
FIG.  LIV.―Dr. Witte examining individual plants of Orchard Grass in the laboratory for constancy                166
FIG.  LV.―Digging pedigree plots of potatoes                170
FIG.  LVI.―Mr. Lundberg crossing potatoes                171
FIG.  LVII.―F1 From different potato crossings                172
FIG.  LVIII.―Digging comparative trial plots of potatoes                176
FIG.  LIX.―Table of yields and starch content of cooking potatoes at Svalöf during the years 1906-1910                180
FIG.  LX.―Two best pedigree potato sorts thus far (1910) produced at Svalöf                181
FIG.  LXI.―Typical landscape of the Plains of Skåne                184
FIG.  LXII.―Showing sheaves of barley put up on stakes to dry after having suffered from three weeks of almost continuous rain                186
FIG.  LXIII.―Map showing geographical position of Sweden in relation to that of Canada                187

PLANT BREEDING IN SCANDINAVIA

I.—INTRODUCTION

There is no subject associated with plant life which is of greater importance yet which is less perfectly understood than that of plant improvement. Efforts to guard against the deterioration of cultivated races date back to the early Romans who, according to Virgil, recognized the need for continued care in preventing the inclusion of variations of inferior value.  The idea of actually improving plants is of comparatively recent origin, dating probably from about the beginning of the nineteenth century. Since that time great strides have been made and it is only with difficulty that one is able to follow at all adequately, the rapid accumulation of experimental data.

While the idea of organic progression had its birth among the early Greeks and while many theories were later advanced by prominent investigators as to the “mode” by which new forms arise, yet it remained with Chas. Darwin to first develop a well supported theory of evolution which he called the “Theory of Natural Selection.” This theory, as is well known, assumes that a constant inherent variation is going on within the race.  Some of the resulting variants will be stronger and will survive, others will be weaker and will perish in the struggle. The Darwinian principle has been widely applied in practice with a view to the improvement of cultivated varieties and not without a certain measure of success.

An enormous impulse to further investigation in the realm of biological science was given by the rediscovery and confirmation in 1900 of Mendel’s famous principles of heredity (25) (first communicated to the Naturalists’ Society of Brünn in 1865, but subsequently overlooked) by DeVries, Correns and Tschermak, subsequently defended and developed as they were by Bateson of England (1). The appearance in tlie same year of the “ Mutation Theory” propounded by DeVries (78) also contributed greatly to a revival of interest in matters pertaining to the great vital problems of natural science.

The views expressed in these theories have served not only to deprive the principle of Darwinism of many of those attributes with which it had been invested but to bring about a vital change in the general conception of the whole phenomena of variation and heredity. These views, together with the degree to which they find either support or contradiction in the experiences of the leading Scandinavian investigators, will be discussed in the following pages.

In seeking support for his theory of “an origin of species by sudden 'mutations’” and in searching for evidence to show the “high practical value of elementary species which may be isolated by a single choice”, De Vries has endeavored to interpret the results obtained at different institutions in the terms of his hypothesis. It was in this way that the Swedish Seed Association at Svalöf, Sweden, was first brought into prominence, especially in America, since in his book “Plant Breeding” (79) published in 1907, DeVries dealt at some length with the work being carried on at that institution. Our thanks are due Dr. DeVries for bringing this work to our attention and for suggesting new and interesting lines of thought and modes of thinking.  Unfortunately, however, the principles of plant improvement now actually recognized by the experts at Svalöf, not being in full agreement with those described by the above author, a wrong impression regarding the work at that place has been spread abroad.

After elaborating upon the composite nature of our ordinary cultivated varieties, as demonstrated by the studies of the men in Sweden, DeVries states his point of view clearly and concisely as follows:—
   “The range of variability disclosed by these new studies is simply so wide that it affords all the required material for almost all the selections desirable at present, and will no doubt continue to be an inexhaustible source of improvements for a long succession of years. They are founded on the principle of single selections, and the range of application of this method is proven to be so extensive as to make all ideas of repeated or continuous selection simply superfluous. It is even so rich in its productiveness that there is scarcely any room left for other methods of improvement; and especially should all endeavors of winning ameliorated varieties of cereals by means of hybridization simply be left out of consideration, as compared with the immense number of more easily produced novelties which this method offers.” (l.c. p. 50).
   The inference here is clear. Our ordinary varieties are composed of a mixture of distinct types. These are so numerous as to render the production of new forms by artificial hybridization quite unnecessary. The problem of the breeder is simply to isolate and propagate the most promising forms and by a process of elimination, finally to locate the best. The discovery of these forms is supposed to be aided by the fact that certain botanical or morphological characters are indicative of or correlated with industrial qualities, thus: “Whenever a distinct quality is desired, either in order to improve a local variety, or to bring it into a form suited for other conditions of soil or climate, or to comply with any other wishes of agricultural practice, it is necessary only to know the botanical marks correlated with the desired qualities. On this basis individual plants may be singled out, and after multiplication through a few years, their progeny will probably respond to the demands made, as soon as the industrial qualities themselves are investigated.” (l.c. p. 277-8).

The work at Svalöf to-day leaves little support for these conclusions.  On the contrary, it clearly indicates that these early opinions were based upon insufficient evidence and incorrect interpretation. As time passed, experimental evidence has accumulated and with it have come new ideas and new modes of thinking, giving birth to new conclusions. The general position held by the men at Svalöf at the present time may therefore be summed up in brief as follows:—
   (a) A progressive system of plant improvement cannot be a one-sided system but must embrace all possible methods of reaching the desired end.
   (b) Artificial hybridization provides an invaluable means of producing superior combinations of characters (sorts) which are not found in nature and this method is now used largely at Svalöf for this purpose.
   (c) The old system of 'mass-selection’ can still be of value in special cases and has never been fully abandoned.
   (d) Superior strains may often be found in a mixed variety, but since these need not necessarily possess striking botanical or morphological characters, their isolation, on the basis of such characters, cannot safely be effected.

A careful study of the development of the work at Svalöf since its inception, is essential to a clear appreciation of the position as above expressed.

II.—THE SWEDISH SEED ASSOCIATION (General résumé).

The Swedish Seed Association was established in April 1886 on the initiative of Birger Welinder, a keen, far-seeing farmer of independent means, operating a large farm near the village of Svalöf.

The aim of the Association, as indicated in the first section of its Constitution, is “to work for the cultivation and development of improved sorts of cereals and other crops and for the utilization of these sorts in Sweden and in other countries.” The Association further aims:
   (a) “To ascertain the value and suitability for our conditions of both native and foreign sorts by means of carefully conducted experiments located at different places.”
   (b) “By means of careful breeding to seek to produce stock seed of special value and to distribute it throughout the country.”
   (c) “By means of exhibitions, literature and other suitable measures to spread information throughout the country and encourage the general use of good seed.”

The various circumstances and conditions which operated in bringing this Association into existence are of more than passing interest.  They are closely interwoven with the social, economic and even the political life of the country. They reveal an antiquated and unprogressive system of land tenure, extravagant and dangerous methods in agriculture and finally an industrial renaissance following upon a realization of the great dangers to the nation of continued disregard of the first essentials of commercial and industrial stability.

Early Swedish Agriculture

While the Agriculture of Sweden is said to date back to the Stone Age, modern Agriculture in that country may be said to have had its birth about the year 1840. From 1840 until about 1870 the growing and selling of cereal grains was the principal industry. Following 1870 an important change in Swedish Agriculture gradually took place. The long period of continuous grain raising began to show its effects in decreased fertility of the soil and as a result the grain growers found that they must change their system and feed their produce at home in order to return to the land at least a portion of the fertility removed by the crops.

Another important circumstance which contributed to the bringing about of a change in method was the great decrease in grain prices, following the extensive importations into Europe of American cereals. The Swedes found that they could not produce grain as cheaply as could the growers of North America, and despite the great difference in distance between the two continents, competition practically forced them to find some other means of disposing of their products.

Experiences of Schübeler

   During the period of large grain exportation, and even later, Dr. F. C. Schübeler (63; 64; 65, p. 145-9), Professor of Botany in Christiania University, Norway, had been conducting very extensive investigations into the effects of a northern latitude and climate upon plant life. He showed that such conditions conduced to produce seed of greater weight, better quality and of earlier maturity due largely to the increased number of hours of sunlight enjoyed by the plants in this northern country during the growing period.  He believed, moreover, that the qualities which were thus acquired were hereditary and as a consequence when seeds grown in the north were sown in southern countries that they would continue to produce plants bearing the same rich, early developing, heavy seed indefinitely. Schübeler’s publications on this question created much interest among the people of Sweden who imagined that nature had thus provided them with a new source of wealth in making possible the establishing of a lucrative trade in grain for seeding purposes with Germany, Belgium, and other countries not so favored.  Many trial samples of seed were sent into these countries for testing, but the results were rather disappointing due largely, it is believed, to the fact that the sorts sent were quite impure, and consequently produced a mixed and unsatisfactory crop. As will be seen later ‘earliness’ is not essentially the product of a northern position, although such a position seems to have decided influence on the weight and quality of seed.

With a view to encouraging the cultivation of a better class of seed grain, several local associations were organized in the early eighties and many continental sorts of wheat, oats and barley were imported into Sweden for trial.  It was hoped that better sorts than those then growing in the country would be obtained and by careful growing under control and under the beneficial climate of Sweden for a few years it would be possible to offer the Southern trade a quality of seed for which a handsome price would readily be paid.  These associations never had more than a local influence and, as a consequence, the period of their activities was of short duration.

During this time Birger Welinder, to whom reference has already been made, had watched the progress of affairs and had studied the situation closely. He believed that the impurity of Swedish sorts had been chiefly to blame for their indifferent success in foreign lands and so conceived the idea of producing seed of pure and constant sorts by a process of continuous selection, crossing and other scientific means, and of making this seed available in quantity to the farmers of his native land. In this way it was hoped that a more rational system of seed production would be developed at home and that eventually there would take place a substantial export of improved Swedish seed to other countries. His ideas seemed logical and were readily and quite widely accepted. The question became a national one and much interest was evinced.

Ably supported by another public spirited gentleman in the person of Baron Gyllenkrook, a large landed proprietor in the neighborhood, Mr. Welinder proceeded to interest others in the work until soon a little band of earnest-minded men gathered together and organized on April 13, 1886, the South Swedish Association for the cultivation and improvement of seeds, with Baron Gyllenkrook as President and Mr. Welinder, as Secretary. At first this Association was intended to affect only the southern part of Sweden, but soon it was seen to be too popular to suffer such restriction and its name was accordingly changed on November 30, 1887, to the “General Swedish Seed Association” with a correspondingly increased scope.

In 1889, another Association (Central Swedish Seed Association) was organized independently at Örebro in middle Sweden, to serve the needs of that part of the country, it being thought that an organization so far south as that at Svalöf could not do justice to the whole land. In 1894 this Association handed over its work to the southern association with the understanding that the latter would extend its activities so as to meet the needs of the central districts. The Association at Svalöf now had a clear field and again changed its name to the Swedish Seed Association which name it still holds.

Membership.

The membership of the Association is composed of honorary members, life members and annual members. The fee for annual membership is five kronor. ($1.35). All members receive the Association’s Journal (Sveriges Utsâdesfôrenings Tidskrift) which is now published, as a rule, every second month, and such other publications as are occasionally edited. In addition to this, the Association assists members in various ways, such as by giving advice on questions pertaining to crop-raising, etc. No actual work is required of members since practically all breeding and selection work is done on the grounds of the Association, either at the headquarters at Svalöf or at the Branch Stations.

Administration.

   The affairs of the Association are administered by the following officers:—
(a) An Executive Council (Mindre Styrelse) consisting of not less than seven and not more than twelve members and three vice-members.
(b) A Board of Directors (Större Styrelse) consisting of the honorary members of the Association, all the members of the Executive Council and a representative from each Agricultural Society which contributes towards the Association. Those societies which contribute more than 500 kronor can elect one representative for each 500 kronor contributed.

Branch Stations.

In addition to the main Institution at Svalöf, the Association has two Branches, one for Central Sweden at Ultuna, north of Stockholm, which works in co-operation with the Agricultural College located at that place, and one for the far North at Lulea where the work is executed in co-operation with the Institution for Chemistry and Plant Biology. The need for more branch stations has long been felt and it is expected that the present number will be augmented in the near future.

Funds.

The revenue of the Association is derived from membership fees, government grants, county grants, contributions from the Agricultural Societies, fees from the Swedish Seed Company on account of stock seed sold the said company and for the inspection and control by the Association of the commercial product. In addition to the above the Association occasionally receives substantial donations from private parties, companies and Associations which are interested in the work.

Experimental Grounds.

The Association possesses at Svalöf about 16 hectares (39½ acres) of land on which are established its buildings, residences and outhouses. The additional land which may be required for experimental purposes is leased from the General Swedish Seed Company, which owns about 3,000 acres adjoining the Association’s grounds.

III.—THE SYSTEM OF PLANT IMPROVEMENT AT SVALÖF AND ITS DEVELOPMENT.

The Method first Employed

When the Association at Svalöf first began its work of plant improvement it adopted the system commonly followed in Europe at that time.  This was known as the System of continuous or systematic selection, the aim of which was, by selection from year to year, to shift the type in its entirety in a certain desired direction. This principle assumed the omnipresence of hereditary variations and, in accordance with the Darwinian idea, it was believed that permanent and substantial improvement might be effected by selecting plants which varied in the direction wished for. In other words, it was thought that continuous selection produced a cumulative or creative effect.

The above principle was usually applied in practice through what was known as the system of “Mass Selection.” By this system, a selection of seed was made from a large number of plants and the whole thrown together and sown “en masse,” in a single plot.

When a sort, by reason of the results of careful testing or for other causes, was chosen for improvement there were taken from the threshed sample from 1,000 to 2,000 kernels for planting in a special plot. The “grading machine” (consisting of a series of sieves) made a discrimination in the size of the kernel, while the “Diaphanoskop” was sometimes used in judging the quality of the sample that should be planted. These kernels were then sown out at definite distances apart by means of the so-called “marker” which consisted of boards fastened together to make a panel about 1.50 m. (59”) long by about 0.50 m. (193”) wide. This was pierced with holes about ¾" in diameter arranged in rows placed 10 c.m. (4”) apart while the holes in each row were 7 c.m. (2.7”) apart. These distances were changed in later years to 15 c.m. (5.9”) and 5 c.m. (2”) respectively. By thrusting a steel punch (Stämpel) through the openings in the board, holes of a certain depth were made in the soil, into each of which a single seed was dropped. By this method not only were the resulting plants allowed to develop evenly, but a study of single plants was facilitated. The adoption of this method of planting having for its aim the reproduction of normal conditions, marked a radical departure from that commonly used by Hallet, Rimpau and many other breeders at that time who planted very thinly, thus allowing an abnormal development. A second departure from the common rule was made in the choice of location for the special plots. Contrary to the custom of the above mentioned breeders who continually sought for locations having extreme fertility, the Svalöf practice was to use only fields which were normally rich and which were in proper place in the rotation.

The Swedish system, which was regulated and controlled by a most exacting mechanical system prosecuted in the laboratory, gradually attained a high state of development under the direction of Th. Von Neergaard, a German mathematician and chemist, who had been appointed leader of the work shortly after the Association was organized. Neergaard had a wonderfully keen, mathematical mind and during his regime some ingenious instruments were devised and a fine system of measuring, weighing and recording both plants and seed was employed. The aim at this time was to exclude the personal element as far as possible and to accept as far as circumstances would permit, the mechanical evidences of superiority.

The first choice of plants was made in the field, the rule being to select only plants which were uniform in length of straw and in general development. Care was also taken to select only those plants which did not produce more than three stalks per plant, the idea being that such plants were likely to develop more evenly, to yield better and to give a product of better quality.  Experience soon showed however, that the degree of stooling could not be taken as a sure indication of the value of a sort; it was only suggestive.

The plants which were chosen from the “élites” were pulled up by the roots, taken to the building and subjected to the searching mechanical examination to which we have already alluded. On the basis of this examination the final choice of seed for new “élites” was made.

Early Laboratory Studies

A closer study of the characters which this laboratory examination took into consideration is interesting. In the first place a selection had to be made of the plants brought from the fields. This choice was based on the average quality and yield of grain per plant, together with the nature of certain botanical characters which were believed to characterize certain groups or types.

A discrimination was next made between the heads or panicles of the chosen plants. Only heads or panicles from the main stems of each plant were taken as it was believed that such heads or panicles offered greater possibilities than did those borne on the lateral and usually less perfectly developed shoots or “stolons.”

The chosen heads were then weighed, it being believed that the heavier the head the larger the kernel and the greater the yield. When the heavy heads had been selected, the next step was to choose those which contained the greatest number of spikelets as it was thought that this was directly correlated with yield. Since long open heads of wheat, barley or rye often produce actually fewer spikelets than the short more compact type and since the latter type was thought to be correlated with stiffness of straw a system by which the specific density of a head, or the number of nodes per 100 m.m. (3.9”) could be expressed, was devised. By this system, the density of the different heads could be expressed in figures and another important basis of selection thus established. The manner in which this system was applied may be explained more clearly by setting the following problem thus:—

   A head of wheat measuring 130 m.m. in length has 24 nodes containing 70 kernels. Problem: What is the density (number of nodes in 100 m.m.) of this head and the number of kernels per 100 m.m.?

Answer:—
In 130 m.m. there are 24 nodes
"   100   "     24/130 x 100==18 nodes.  Specific density = 18
(This was commonly expressed as "D. 18").

In 130 m.m. there are 70 kernels
"   100   "     70/130 x 100 = 54 kernels.

In order that the density of a large number of heads might be quickly determined, Neergaard devised the first automatic classificator used at Svalöf. This obviated the necessity of working each case out on paper as above.

The choice of heads having been effected, the next step was to choose the best kernels. In accordance with the old idea that these were to be found near the centre of the head in wheat, barley and rye, and in the upper part of the panicle in oats, only kernels from these places were taken for seeding.

The use of sound, plump and large sized kernels for the sort was insisted upon. The importance of this practice has never been challenged.

A further selection of kernels was sometimes made on the basis of quality, an expression of which was sought by means of the “Diaphanoskop,” an instrument which made it possible to compare the “mealiness” of different kernels by placing them over openings through which the light might pass according to the transparency of the kernel. A hard, glassy and therefore more transparent kernel in wheat was considered of better quality than a mealy, opaque kernel, while in barley the latter type of kernel was believed to be more suitable for the brewer.

Final valuation of sorts

The final valuation of a sort must naturally depend largely upon field trials and a laboratory analysis of the product. Such trials and analyses have occupied a prominent place at Svalöf from the beginning and will be discussed more in detail later.

Results from Continuous Mass-Selection.

Efforts to develop a strong-strawed type of Chevalier Barley by mass-selection

During the first period in the development of the work, efforts were naturally directed toward the alleviation of the most pressing needs of the farmers. Among these needs was that for a Chevalier barley with a stiffer straw. This sort was considered at the time to be without an equal in quality for brewing purposes but had the one serious defect of lodging under comparatively slight provocation. Repeated selections were therefore made of those plants which possessed heads of the greatest density in accordance with the prevailing idea that a definite relation existed between density of head and strength of straw. All attempts in this direction however proved futile and were finally abandoned. This failure is attributed to the fact that the Chevalier in question was a pedigree sort produced by Hallet of England and as such, possessed a degree of constancy which precluded the possibility of effecting improvements by means of the system practised. On the other hand, had this sort actually been a common mixed variety it is doubtful if any progress in the desired direction would have been made since it has been shown that no absolute relation exists between compactness of head and strength of straw. Thus the failure to produce a stiff strawed Chevalier by continuous mass-selection cannot be accepted as an evidence of defects peculiar to this system alone although DeVries has regarded it as such (79 p. 64).

Development of Clay and Moss barley

Other selections of heads of varying specific densities were made from the Native Plumage barley. “This variety,” says Bolin, “was found to contain 10 to 12 different classes in regard to density of head while the different plants showed corresponding differences in manner of growth and structure of straw” (5 p. 60). Thus in 1888 approximately 1000 heads were selected and divided into two main groups representing the two extremes of density while a third group represented the average density of the whole number (See Fig. 2). In the group containing the most open heads the density averaged from 40 to 41 and the seed of this group was taken to plant plot XII1, in the Spring of 1889. In the group containing the most compact heads the density averaged from 45 to 48. The seed from this group sowed plot XII11 in 1889. The group representing the average condition of the whole 1000 heads in regard to compactness averaged 42 to 44. This group sowed plot XII111. An examination of the table will indicate the performance of each group in succeeding generations and will reveal the interesting fact that from the group possessing the most open heads in the beginning there was ultimately produced a sort (0501) which remained relatively lax, while the group possessing the average density of the whole 1000 original heads was found at the end of three years to have an average density identical with that of the most densely headed group. From the progeny of the latter group a sort (0502) was produced which had a denser head, ripened about 10 days earlier and produced a lower yield than 0501. It also possessed a peculiar dark grey color of stem and leaf. Both 0501 and 0502. which received the name Clay and Moss respectively, belonged to the Erectum type although the former possessed a decidedly nodding (Nutans) head. This is a good example of a sort with a nodding head actually belonging to the Erectum group and indicates clearly why the position of the head cannot be taken into consideration in a system of classification (See classification of barley types page 133).


FIG. II.—Two Mass-Selected Barley Sorts.



FIG. III.—PEDIGREE OF CLAY AND MOSS BARLEYS.

The development, or more properly the separation of the above two barley types affords an excellent illustration of how selection en masse may be effected. The only necessary condition in order that such separation may be made is that different hereditary forms be present and that these present differences in respect of the character sought. In the case in question this success was due to the existence of different forms possessing different specific head-densities. By the annual selection from each group of those heads, the density of which approached most nearly that which was desired, there was gradually eliminated the ‘transgressive’ or ‘overlapping’ forms until at the end of the fourth year two groups representing the two types mentioned remained.

This explanation of the separation of the two barley sorts Clay and Moss, affords an argument that at least some of our common varieties are composite in character and are capable of being divided into their component parts which in turn may possess different values.

A similar example of how it may be possible to effect gradually a separation of two distinct types by mass-selection is to be found in an experiment conducted some years ago at the Experimental Station at Tystofte, Denmark, and described by Tedin (66 p. 23) in the journal of the Swedish Association.  The primary object of this experiment was to determine the comparative values for seeding purposes, of large and small kernels in the case of barley and oats. Both the large kernelled lot and the small kernelled lot required for this experiment were obtained from a mixed variety, and in each succeeding generation the sample of large kernels required to continue the test was obtained from the plot sown with large kernels while the small kernels were obtained from the plot produced from small kernels.  This practice was continued for a number of years with the result that, to the surprise of those interested, two apparently quite distinct types were finally separated.

The inference in this case must also be that the original varieties were composed of different strains, some of which were normally small kernelled and some large. By continuously taking only the small or large kernels, as the case might be, from their respective groups, all transgressive forms in respect of the character concerned, were gradually eliminated, with the above result.

The principal object of the work at this time being to produce pure, constant and uniform sorts,” great care was exercised in selecting plants which corresponded as closely as possible with a given type. Due attention was therefore given to all botanical marks which might aid in this direction.  Thus in seeking to produce pure stocks of barley, certain marks on the kernels were found of assistance. With the help of these marks, which proved to be the basis of the present system of classification for barleys in use at Svalöf and which will be described later (See page 133), a relatively pure stock of two old sorts (Chevalier and Prentice) was produced and placed on the market in the early nineties (29, p. 10). Relatively pure stocks of other sorts such as Swedish Plumage barley and Black Tartarian oats, soon followed, while in 1895 a stock of improved Prentice barley which received the name Princess, another of Awnless Probstier oats and still another of Renodlad (Selected) Squarehead wheat, were given over to the General Swedish Seed Company for propagation and distribution. The development of the three last sorts is interesting.

Development of the original Princess Barley.

In the case of Princess, Bolin (6, p. 113-14) isolated three groups of forms from the old Prentice variety of barley, each of which groups possessed certain prominent characters. The most prominent characteristic of one of these groups was said to be the peculiar arrangement of the lateral rudimentary kernels which, on one side of the head near the tip, assumed an almost upright position. From this group was obtained the original Princess barley a stock of which was given over to the General Swedish Seed Company in each of two years (1895-1896) and which quite displaced the old Prentice.

The superiority of the new sort over the old is said to have been in its striking uniformity in height and color of plant and in its higher yield. For the average of the four years 1894-97 it gave decidedly higher yields than Prentice which came next among all sorts tested (30, p. 136).

A pedigree sort out of Prentice displaced the mass-selected sort Princess about 1897 on account of the belief that pedigree sorts must be better than composite races. The results do not show however, that pedigree stocks out of the variety mentioned, actually excelled Princess in yield.

Origin of Awnless Probstier Oats

The first attempts to develop an awnless strain of oats were made soon after the organization of the Association, the common Probstier variety being chosen as foundation material. The presence of awns was regarded as not only detracting from the appearance of a sample but also preventing the grains from packing closely in the measure, thus reducing the weight per bushel. The first efforts in this direction led to no results when finally, after several different courses had been tried, it was decided to reject all plants which had the slightest appearance of an awn on any of the kernels and which were not sound and entire with not a single kernel missing. These later attempts proved successful in producing an awnless sort which received the name ‘Awnless Probstier'. This sort showed not only greater uniformity than the old sort, but also during the years 1893-96, when the two sorts were competing in the comparative trials, it gave a little higher average yield (33, p. 178). For these reasons it soon came to practically displace the old sort and, even to-day, stands among the highest yielders in Sweden.

Origin of Selected Squarehead Wheat.

   Renodlad (Selected) Squarehead wheat was produced by mass-selection after the severe winter of 1891, when a selection was made of the best of those plants which had survived (See Fig. 4). A quantity of this stock was given over to the Seed Company in 1895, since which date several renewals have been made from selections following such severe winters as 1899 and 1901. By these repeated selections the proportion of hardier Squarehead individuals within this variety, according to Nilsson-Ehle’s reports (39, p. 272; 51, p. 73) has gradually increased until now this is among the most hardy of the high yielding sorts. Indeed up to the present, no sort has been found more suitable for certain large districts in Sweden. In yielding tests at Ultuna, since 1904, it has given the highest average yield of any disseminated sort originated by the Association.

The efforts to effect improvements upon certain old varieties of cereals by the system of mass-selection as applied at Svalöf were therefore by no means without results. Greater uniformity, higher yielding capacity and, in autumn wheats, greater hardiness were the ultimate rewards of these endeavors, although it required several years before the extent of this improvement became fully demonstrated.

Introduction of the Pedigree Culture system of Selection at Svalöf.

After the Association had been in operation for about five years Prof. Hjalmar Nilsson succeeded Von Neergaard as director. As first assistant to Neergaard, Nilsson had closely followed the progress of the work and had made many valuable observations. He had carefully studied the different appointed cultures in the field and had noted the regularity with which many different botanical types appeared from year to year. In assuming the leadership he at once set to work to separate out with extreme care all plants which were botanically or morphologically different in the slightest degree. Thus during the harvest of 1891 a large number of heads from many different varieties of autumn wheats were collected as were also plants of vetches and pease.  These were subjected to a most critical examination in the laboratory where several hundred apparently distinct types (200 of wheat and about 1,200 of vetches and pease) were sorted out, described and numbered. In many cases each of these types or groups was made up of many individuals. In a number of cases, however, certain forms were found which had no duplicates. Each of such forms was therefore required to represent a group in itself. Each group was now allotted a separate plot, careful records being kept of the character and number of individual heads or plants as the case might be, which comprised the progenitors of each culture.


Photo by courtesy S. S. Ass'n.

FIG. IV.—Svalöf’s Selected (Renodlad) Squarehead Wheat. (Mass-Selected Sort.)

A careful study of the resulting harvest did not at first suggest any solution to the problem when by mere accident an observation was made which served to place the whole question in an entirely new light. Of all the hundreds of cultures under consideration only those few which came from a single head or plant produced a uniform progeny. This observation seemed to indicate without question, that the quickest way, if not the only way, to obtain a uniform sort was to begin with a single plant. It was therefore decided, after the corroborating results of another year’s investigations had been obtained, that henceforth all work must be based on this principle, the single plant to be the unit for improvement instead of the ‘group.'  This method had already been used by Vilmorin of France and is now popularly known throughout Europe as the ‘Vilmorin System of Selection,' although at Svalöf it is usually referred to as the System of Pedigree or Separate Culture.

Form Separation on the basis of correlations

The basic principle of the new system was to separate out the greatest possible number of distinct botanical forms, to propagate each of these separately and, by a process of elimination, finally to isolate the best.  This idea of form-separation (“Formentrennung”) as a means of discovering superior individuals as starting points for new races, had been applied by LeCouteur and Patrick Shirriff of England many years before, but at Svalöf it was introduced on a much greater scale.

While the system of separate culture was therefore not new, yet the credit of devising a new method of application was claimed by Svalöf. This method consisted of basing the selection of mother plants upon assumed ‘correlations’ between botanical characters and industrial qualities. Great weight was attached to such points as the position of the branches in oat panicles, the number of kernels in the spikelets and the density or closeness of the head in wheat and barley (34 p. 50). The question of correlations will be dealt with more in detail later (See page 31).

Classification of Forms into Groups.

In order to facilitate the handling of large numbers of distinct botanical forms a system of classification was devised by which it was sought to arrange the different types into sharply defined groups. Thus in wheats 7 types were distinguished chiefly on the basis of the shape and density of the head; in oats 5 main types were described while in barley 12 types were named.

System of numbering the different sorts.

A system of numbering the different sorts was also devised which would indicate at once the general type to which each belonged. Thus an oat sort belonging to type 3 was given a number preceded by the figure (3). This in turn was preceded by (o) to distinguish it from ordinary numbers.   Victory oats for example, is registered under the number 0355, which indicates that this sort belongs to type 3. The figures (55) indicate the number of the individual sort itself. This system was of great assistance so long as selection was confined to botanically different forms but when the practice later became to select large numbers of individuals from certain old races without special regard to botanical or morphological characters it naturally played a less important part.

Pedigrees still selected from pedigrees.

With the introduction of the pedigree culture system there did not follow immediately a rejection of the original principle of continuous selection.  The new system was regarded useful only as a means of obtaining in the shortest possible time, constant and uniform sorts. The Darwinian idea of the omnipresence of hereditary variation in all life was still held by Nilsson who regarded it necessary to continue the selection from generation to generation in order to effect a complete fixation of the characters, while at the same time he believed that continuous selection was still capable of effecting improvements even upon sorts already fixed (32, p. 13). This idea came to be abandoned in due time when it was discovered, as we shall see later, that the variations which were often noticed in these small plots were mere modifications, induced by abnormalities in such external factors as soil, moisture, etc., and that these were not hereditary.

Absence of hereditary variations in pedigree cultures. & Theory of unit-characters.

The appearance in 1900 of the views expressed by Mendel and DeVries, together with those communicated in 1903 by Johannsen (14), the noted Danish investigator, served to place the whole phenomenon of variation in an entirely new light and seemed to explain at once, in a most convincing and logical manner, the main circumstances upon which the occurrence of hereditary variations depends. The principle involved in these views is that a plant or animal is composed of distinct and independent Unit Characters, units because they are capable of being treated as such. These units were regarded by Bateson as corresponding, in a sense, with atoms in chemistry.  While their nature is still a subject for speculation, this author (2 p. 266) suggests that the operations of some units may be carried out by the formation of definite substances acting as ferments. By the recombination of unit characters through hybridization new ‘compounds’ or combinations may be effected which may appear and act quite differently. The characters entering into such a combination, however, are not themselves affected, but may be separated and recombined by future crossing to form other combinations equally distinct in character.

If this theory of the unit constitution of individuals be correct then hereditary variations must obviously arise either directly as spontaneous changes (“mutations”) or as the result of the combination and subsequent segregation of unit characters through hybridization.

Johannsen’s pure-line theory.

In his classical researches in connection with problems in heredity, inspired as they were largely by the work of Vilmorin of Paris, Johannsen showed the scientific necessity of working with what he termed pure-lines when seeking to establish first principles. By a pure line he means the progeny of a single, self-fertilizing individual. His investigations served further to modify previous conceptions of heredity as expressed in Galton’s “Law of ancestral heredity.” Galton (13) worked with “crowds” or populations of individuals and annunciated that the general type of a given crowd can be changed or “shifted” by the selection of variations of a specific character (plus or minus variants). Johannsen’s investigations were conducted with pure lines, that is the progeny of single individuals within a crowd. The plants chosen were beans and barley, both of which are normally self-fertilized and therefore easy to keep pure. The constituents of all pure lines worked with showed normal fluctuations which grouped themselves around the mean in accordance with the “Law of Quetelet.”  Certain of those constituents which deviated farthest from the mean in regard to certain characters, were selected and propagated separately but instead of producing a progeny identically similar to the mother plant in each case, they showed a regression to the original type of the line. Extensive experiments finally induced Johannsen to conclude that continuous selection within pure lines is unable to produce permanent changes. In other words, he concluded that there is no hereditary variation within pure lines, and therefore no possibility of effecting permanent improvements in a self-fertilizing race by means of such variation. He did succeed, however, in isolating an occasional product of what he regarded as a “mutation” or sudden variation which appeared as something “new.” Should such fortuitous germinal variations arise frequently it would seem possible to obtain results by careful continuous selection along definite lines. Since however, such variation might be extremely small and neither meristic nor morphological in character, it would be extremely difficult to determine whether or not any definite progress was being made. Only the best statistical methods would suffice and even then the opportunities for experimental error would be such as to. render it almost impossible, except perhaps over a long series of years, to form any conclusion which would be above scientific criticism.  Up to the present all efforts put forth in Scandinavia have failed to show the utility of continuous selection as a means of effecting improvements of a permanent nature in pure lines.

Johannsen’s work has contributed greatly to our knowledge of selection by revealing the existence of pure lines, biotypes or “genotypes” as he sometimes calls them. He has demonstrated that continuous progress need not be expected by basing selection upon Galton’s Law since a population, consisting as its name implies, of biotypes of different means cannot possess a biological mean. The so-called variations of Galton and Darwin, in so far as these concerned self-fertilizing plants, would therefore seem to be simply distinct biotypes which, on being propagated separately, breed true. By avoiding accidental crossing, which even in the so-called “self-fertilizing species” is known to occasionally take place, the constancy of these lines may be fully maintained. These conclusions received much support from the work at Svalöf, at which place experience seemed to show more and more conclusively that if hereditary variations did exist in pure lines they were rarely to be found, at least by mere plant inspection.

Many interesting examples are on record at Svalöf of efforts being put forth to find within these pure cultures, the starting points for new and better sorts. Thus, many apparently aberrant individuals were taken out and propagated separately, but in all cases they proved to be mere transient modifications as they failed to reproduce the special characters for which they were selected. In 1900, according to Nilsson-Ehle, an aberrant oat plant which seemed to give promise of marking an advance over its host, was found growing in a certain pedigree culture having the stock-book number 0385. This plant had three kernels in each spikelet, while the sort 0385 was characterized by two. The kernels were described in the records as “actually appearing better, more oval, plump and of better quality.” The above plant was selected and its seeds sown the following year when the progeny still seemed promising. In 1902, seed from the preceding year’s crop was sown on a larger plot when not a single “three-kernelled” plant was to be found and the attempt was therefore abandoned.

In 1900 an oat plant possessing a particularly stiff upright panicle was found in a sort (No. 0955) having a panicle which was weak, drooping and presumably of quite an inferior type. This stiff-panicled individual was selected and its seed sown in a small pedigree plot in 1901, but instead of producing all stiff-panicled plants it produced a weak-panicled progeny of quite the same type as the parent sort.

Individual winter wheat plants which survived certain unfavorable winters and springs to a marked degree, have been selected from pedigree cultures which, as a whole, had suffered more or less severely. On propagation it has been found that these do not mark any permanent improvement in hardiness over the mother sort. They have thrived under adverse conditions simply because of influences which were purely external (35 p. 176).  In composite races (mixed varieties) the case is naturally different as here there may be found a ‘collection’ of distinct strains some of which may be normally hardier than others. In such cases the fittest will survive and in this way render the variety more hardy.

Many other examples might be cited to show the apparent futility of seeking to find at least within the first generation pedigree plots of normally self-fertilizing species, individual plants which are capable of producing better progeny than others within the same plot, but probably those already given will suffice. It should be noted in passing however, that repeated selections from larger cultures even of pedigree sorts are still made in the case of wheat, but such selection is not based upon the Darwinian idea of variation as we shall see later.

Necessity of working with an extensive material.

Following the discovery of the composite nature of common varieties and the consequent introduction of the pedigree culture system, it was soon seen that a very extensive material must be worked with in order that the chances of isolating superior individuals might be as great as possible. There were therefore collected hundreds of apparently distinct botanical forms, each of which was sown on a separate plot. In making this collection of forms little attention was paid at first to the standing of the variety in which they were found. Samples of seed were also collected at exhibitions and by correspondence with interested farmers and others while members of the staff took advantage of journeys into the country to collect promising looking plants from fields.

Early ideas re artificial hybridization

As a means of increasing the tendency to the production of “new spontaneous variations” (34 p. 56) according to the old idea as expressed by Nägeli, artificial crossing was introduced about 1893. In the absence of any guiding principle such as is now available, this work did not occupy an important place but was regarded as of quite secondary consideration and almost wholly of theoretical interest. Indeed it was believed that the old races contained a sufficiently rich material to meet practically all demands.

Restoration of the personal element in breeding work. [&] Specialization of the work

The new method being based on the isolation and separate culture of distinct botanical forms there was necessitated a most careful study of these throughout their entire life history.  This fact served to restore the personal element which the mechanical system had sought in vain to displace. The breeding various classificators, automatic weighing machines and other mechanical devices to which so much importance had formerly been attached were largely dispensed with. The importance of specialization being more fully recognized, additional experts were employed and allotted certain crops as their specialty. All their attention and study was to be devoted to the improvement of those crops for the success of which they were made responsible.  Dr. Hans Tedin was engaged in 1891 as specialist for peas and vetches, Mr. Phr. Bolin was allotted the barleys in 1892 while Prof. Nilsson himself kept wheat and oats as his specialty until 1900 when, on account of the time required to attend to the duties of a large and growing institution, this work was handed over in its entirety to Dr. H. Nilsson-Ehle who has continued it since that time. Rye was added to the list later with Mr.J. N. Walldén as specialist. This gentleman subsequently resigned and was succeeded by Mr. Erik Ljung, who occupies the position at the present time. More recently (1904) potato breeding has been taken up with Mr.J. F. Lundberg as specialist.  In 1905 grasses and clovers were added to the list, Dr. Hernfrid Witte being appointed head of this department in 1907. About 1909 work in the breeding of field roots was initiated with Mr. Ivar Karlsson in charge.

Correlation or the Association of Characters

With the introduction of the new system each specialist set to work to study his plants thoroughly. All botanical and morphological characters, down to the minutest detail, were investigated and elaborate annotations were made and arranged in order. If certain visible characters were indicative of industrial value as was then supposed, it was obviously the first concern of the breeder to determine such and to use the knowledge so acquired in the isolation of new mother plants. The degree of constancy displayed by the various pure cultures in respect of the development of these characters seemed to indicate clearly that the latter must offer a reliable basis of distinction. Such an assumption seemed natural and logical and served moreover to make the way appear clear and relatively simple.

As time passed many interesting conclusions came to be drawn as to the relationship which was believed to exist between certain external characters and industrial qualities.  A few instances may here be given. In oats different position of ‘pure lines’ or strains may often be distinguished by the character of the branches in panicle.  In those forms having spreading panicles four main types may be oat panicle defined thus: (1) Stiff, upright panicle; (2) Panicle pyramid-like with long, slender weakly rising branches; (3) Widely spreading panicle and (4) Panicle with branches weak and drooping (See Figs. 5 and 6). In addition to these four branching types, the common side-oat type, originally classifiedas a distinct species (Avena orientalis Schreb.), forms a fifth. In comparing these types with the industrial values of the sorts it seemed to be shown that the group in which the panicle assumed a more rigid upright position was as a rule the most productive. Such a conclusion, however, has had to be modified since investigation of the tables of yields of the different sorts over many years shows that among the stiff panicled sorts are to be found many which are among the lowest average yielders of all those tested. As instances, may be mentioned the sorts having the stock-book numbers 0310, 0326, 0404 and 0452. There cannot therefore be accepted as an infallible guide, any definite type of panicle.

oat panicles        more panicles
FIG. V.―Types of Panicles in Oats,―a, stiff upright; b, drooping.        FIG. VI.―Types of Panicles in Oats,―c, broad, widely spreading; d, narrow ovoid with irregularly bowed main branches.


Relation between compactness of head and strength of straw.

In wheat and oats the character of the head was believed to be associated with strength of straw, investigations seeming to show that a dense, compact head and a stiff, strong straw go together. Here again numerous exceptions have caused this idea to be modified.

Relation between number of kernels in the spikelet, and yield and quality.

Highly interesting investigations into the relationship between the number of kernels in the spikelets of oats and wheat and the yield and quality of the crop were made by Nilsson during the years when these crops were under his direct charge. The number of kernels in a single spikelet of oats is usually from one to two, although three is not uncommon. In wheat as many as six may be found, although from three to four is generally the case. For purposes of investigation Nilsson defined three classes of spikelets: three-kernelled (S3), two-kernelled (S2) and one-kernelled (S1). These are illustrated below.


FIG. VII.—Different Classes of Spikelets. (Author del.)

It would seem natural to conclude that in spikelets such as S1 which contain but one kernel (a) that this would be larger than kernel (a) in S3 which contains three kernels. The following, however, was found to be the rule:—
   1. “That the development and weight of each kernel stand in a striking and significant relation with the number of kernels in the spikelet; but
   2. “That with a rising number of kernels there is associated a considerable increase in weight per kernel instead of the opposite which one would expect.
“Kernel (a) is never so small and miserable as when it is alone as in S1 and never so heavy and well developed as when it is accompanied by two other kernels as in S3 (27, p. 18; 28, p. 183).

This striking fact is clearly demonstrated in the following table which gives the weight of each kernel in the three-kernelled spikelets, in two-kernelled spikelets and in one-kernelled spikelets found on the one plant in each case:

Types InvestigatedAverage weight per kernel in milligramsPer cent of each
class of spikelet
in plants studied
In three-
kernelled
spikelet
(S3)
In two-
kernelled
spikelet
S(2)
In one-
kernelled
spikelet
(S1)
abcabaS3S2S1Total
Plants from Probstier type543814.804428.2533.5014824100
Plants from Ligowo6042.816.7552.6332.7031.0013834100
Plants from side-oat types50341038.1320.2327.93117415100
Plants from new types of stiff-panicled black oats50.6630.169.3340.4122.6827.089829100

As a result of his investigations Nilsson concluded that “oat sorts having the highest number of kernels per spikelet are decidedly the most valuable” (27, p. 19 and 27). The same conclusion was arrived at in wheat, thus: “Even in wheat the highest possible number of kernels per spikelet is an especially desirable character, as it carries with it an improved crop not only in respect of quantity but still more in quality” (28, p. 205). In arriving at these conclusions Nilsson made certain reservations, thus:  “It now remains for a series of years’ testing in larger practice finally to confirm or disprove my here expressed opinion” (28, p. 210). Fifteen years have passed since the above statement was made and it is now only necessary to compare the best sorts of to-day with the number of kernels per spikelet by which they are characterized in order to determine the correctness of these early opinions. Thus the two best oat sorts at Svalöf at present, viz.:— Victory and Gold Rain, are classified as two-kernelled sorts. On the other hand certain other high yielders, such as Danish Nasgaard are, with relative regularity, three-kernelled. Conversely it has been found that certain relatively low yielders, such as Hvitling and 0313 are also three-kernelled sorts, while others again, such as White Probstier are classified as two-kernelled.  There seems therefore to be no definite relationship between the yield of a given strain and the number of kernels per spikelet by which it is characterized.

As regards quality (absolute weight of kernels and percentage hull) the two-kernelled sort Gold Rain stands in the foremost rank, being especially noted for its high weight and low per cent hull.  The number of kernels per spikelet by which sorts are characterized cannot therefore be regarded as an indication even of quality.

The present attitude of Nilsson-Ehle and Tedin toward this question is that a large number of kernels to a spikelet is indicative of higher yield only in the case of fluctuating individuals within one and the same pure line, but is of no special significance when it concerns the variety as a whole.  This may at first seem contradictory but one must keep in mind that yield is the product of many different factors, so that it is quite possible for a sort having many kernels to a spikelet to still give a relatively low yield. Interesting investigations in Germany by Böhmer (4, p. 50) and in Norway by Christie (10, p. 39) seem to confirm these conclusions. Christie worked with ten pure lines of Norwegian grey oat, fourteen of Norwegian white oat and eighteen of Probstier oats during 1909 and 1910. His studies show that the greater the number of kernels in the spikelet the greater is the weight of kernels per plant in the case of different plants within the same pure line, but in the case of different pure lines this relationship is not shown. “In comparing pure lines from the same old variety of oats I do not find,” he says, “any reason to attribute any special value to three-kernelled spikelets. The absolute weight of kernels per plant gives much more certain information regarding the productivity of the stock and is, moreover, essentially quicker and easier to determine.”

While the value of different strains cannot be judged by the number of kernels which are borne by each spikelet, yet a distinction can often be made on this basis between different lots of the same strain grown under different conditions.

Environment plays an important part in determining the number of kernels borne in the spikelet. Under certain conditions a sort which is normally three-kernelled will develop only two-kernels in a large percentage of the spikelets. Conversely a sort which is ordinarily classified as two-kernelled may sometimes produce a large percentage of three-kernelled spikelets.

Relationship between date of maturity and yield.

It has long been held by many that early maturity and high yield are antagonistic or, in other words, that high yield and late maturity are correlated. This idea has had to be modified considerably within recent years owing to the appearance of a number of high yielding yet early maturing sorts. Thus at Svalöf Sun wheat, Hannchen barley and Gold Rain oats, all high yielding sorts, are nevertheless relatively early maturers.

Origin of Primus Barley.

As an example of the course of procedure followed when attempting to isolate distinct botanical forms as mother plants on the basis of correlations, there is cited in one of the station journals (34, p. 51) the isolation of a form of brewing barley which afterwards received the name Primus. The account of the origin of this sort, as given in this article, is substantially as follows:—
   Efforts to obtain a stiff strawed sort from the high quality but weak strawed Chevalier having failed, attention was turned, about 1893, to a stiff-strawed but poor quality “Imperial” barley with the hope that this perchance, might include forms having the short-haired rachilla of the Chevalier kernel (which was supposed to be correlated with high brewing quality) and at the same time possessing the strength of straw of the Imperial.  Thousands of plants were examined and out of these a few dozen were discovered which showed the desired character. These were planted out in separate cultures and their progeny studied with the result that eight years later (1901) the progeny of one of the best of these came on the market under the name Svalöfs’ Primus, (0706).

The above account has been cited by DeVries (79) “as an illustration of the high significance of these correlations,” a citation which has been widely quoted in America. An examination of the origin of the mother sort from which Primus was taken, however, seems to throw an entirely different light on the situation and to nullify the arguments presented as to the value of correlations, at least in so far as this particular case is concerned. Thus the so-called “Imperial” barley referred to as the mother variety of Primus was imported from Germany for testing at Svalöf under the name Diamond.  This was originated by Bestehorn of Germany and listed in the German seed catalogues as a crossing product of certain parentage. The opinion that this sort was actually of hybrid origin was expressed by Bolin (5, p. 61) in 1893 and later (7, p. 10) was more fully discussed by the same author in one of the leading periodicals of Sweden, substantially as follows:—
   "Among the various barley sorts imported from Germany for testing at Svalöf was one known as the Diamond barley. This was said to be a crossing made by Bestehorn, a German breeder, between a Nutans form (probably Chevalier) and Imperial which belongs to the Erectum type. The hybrid Diamond was found to be mixed (unfixed) the majority of the plants resembling Chevalier. Among the whole population were found a few plants, the kernels of which showed a union of the short woolly-haired rachilla of the Chevalier with the peculiar character of the base of the kernel of Imperial and thus were regarded as the result of a true crossing between the two. The plant from which Primus originated was one of these"

If this sort is actually a crossing product, as Bolin insists, it affords an excellent example of the value of hybridization as an aid to the breeder. At the same time the circumstances which surrounds its origin, together with the fact that sorts which have the supposedly undesirable character of kernel have proven quite as satisfactory for brewing as have those which were regarded as especially suitable for this purpose, deal a severe blow to those who have sought to show the importance of correlations in forming direct judgments as to practical values.

Speaking of these correlations in barley Tedin says: “I do not believe in the existence of correlations between different simple characters by which a certain character is said to indicate the nature of another, but regard such as being simple manifestations of the same unit-character" (73, p. 8-9).

The inability to judge practical qualities from other characters in accordance with the idea of correlations is also pointed out by Johannsen (16), Kølpin Ravn (58) and other workers of recent years.

Weight per 1000 kernels vs. yield
In Denmark important investigations into the question of correlations have been prosecuted for many years. A few examples will here be cited.  As is well known by all breeders, different pure-lines or strains have their own characteristic weight of seed. That no relationship exists between weight per 1000 kernels and yield is clearly shown by Vestergaard of Abed Experimental Station, Denmark, in the following table (80, p. 51):
[Grain Type]Sorts arranged according to yieldWeight per
1,000 kernels
(Grams.)
Autumn wheat
Squarehead
45
Golden Drops
47
Kolbe
45
Urtoba
54
Kent
50
Gl. Danish
43
Two-rowed barley
Prentice
47
Chevalier
46-47
Native
47
Goldthorpe
52
Crossing
53
Imperial
54
Oats
No. 45
36.3
No. 39
34.2
Danish
35.0
White Banner
32.2
Beseler -0
35.0
Ligowo -5
36.5

Twelve oat sorts grown at Svalöf are arranged below according to yield.  Opposite each sort is given its corresponding standing as regards weight of kernels:

According to yieldAccording to
weight of
kernel
No.  1No. 10
  2 7
  39
  45
  54
  66
  711
  82
  93
 101
 1112
 128

From the above tables it will be seen that some of the most valuable strains possess only medium sized kernels. This fact at once exposes the danger, when dealing with an ordinary variety which may consist of large, medium and small kernelled strains, of over-sorting or grading, that is retaining for seeding purposes only the very largest kernels. In such cases a uniform sample of plump, medium sized kernels should be sought for.  The use of pure strains of course obviates this difficulty entirely and herein lies one of the many advantages of such strains.

Size of head vrs. yield [&] Dangers associated with mass selection

In selecting heads of grain by mass-selection from mixed races with a view to increasing the yield the natural tendency is to select the largest.  This is shown to be an unsafe practice. As is size of kernel so is a sort-character. Certain pure lines of outstanding value have been found to possess a relatively small head while many inferior strains are characterized by strikingly large ones. In other words there seems to be no definite relationship between size of head and yield. A few examples will suffice to show this: In barley, Princess and Chevalier though high yielders, have relatively small heads while Imperial and many other inferior sorts have heads of large dimensions. In wheat, English Stand Up and Tystofte Small which are among the most productive sorts, are noted for the relative smallness of the head.  The continued selection of extra large heads from a composite race which happens to contain both large and small headed strains can therefore easily prove an injury rather than a benefit. An excellent illustration is afforded by Vestergaard, in his investigations with the common Prentice barley (l.e. p. 106). Out of this variety there was isolated, among others, a certain group representing 4—6%, of the whole and which was characterized by long coarse straw and large heads. A comparison between pure lines from this group and from the mother variety is given below as follows:

Yield of
grain per
Td. Ld.
(about
1 acre)
kilograms
Length of
straw in
c.m.
Length of
head in
m.m.
Weight of
100 heads
in grams
Per cent
of shoots
bearing
heads
24 Pure lines from the common Prentice type435089.577.868.474.6
8 Pure lines out of the long strawed large headed group407693.384.080.967.0


A mass selection of heads from the long strawed, long headed group would obviously lead to decreased yield in this case.

Stooling in grain vrs. yield and quality

The question of stooling or the developing of ‘side shoots’ in cereal grains and its relationship to yield and quality has also been investigated. As most growers know the power to ‘stool’ varies more or less with different sorts. Under certain circumstances this characteristic may be of considerable practical value. Thus where the stand is thin as a result either of thin seeding, the attacks of disease or insects or of some other agency, the power to stool and thus in a measure at least to compensate the loss, is obviously a characteristic of importance. Sorts which normally de velop several straws from the one seed have long been regarded by many as superior to those in which the stolons are more sparse.

Prof. E. Schribaux of Paris, and certain other workers, however, have expressed opposite views. Schribaux (60) claimed that the so-called ‘main’ stem reaches the best development and produces the most grain and the best quality, thereby being of greater value than those which develop later. Later, investigations of Rimpau (61) and Lippoldes (21) indicate the weak points in Schribaux’ work and the incorrectness of his conclusions.

When the work at Svalöf was begun it was insisted that no plant of more than three stems should be selected and that these be as evenly developed as possible. This rule led to no results of special significance and so was finally abandoned. With the introduction of the pedigree system a large number of pure lines came to be studied thereby providing excellent opportunity for further elucidation of this question. As time passed Tedin observed in barleys that certain sorts which one year were recorded as “heavy stoolers” were other years designated as “light stoolers” and vice versa.  This and other perplexing irregularities induced him to submit the whole question to a thorough investigation which covered the years 1903, 1904, 1905 and 1907 (74 p. 292). The conclusions drawn from these investigations are that while a given sort may possess its own stooling propensity yet this, especially in the case of barley, plays so small a part in comparison with the effects of life-conditions as to be almost unworthy of mention. On the other hand more marked differences are shown to exist between sorts in respect of their manner of stooling. In some sorts for example the side shoots develop very unevenly while in others the development is uniform, thus allowing even maturity and conducing in a large degree to good quality. Such a sort is obviously to be preferred.

In 1903 careful observations were made by Nilsson-Ehle respecting the stooling properties of different oat sorts. A few examples taken from the records are given as follows:—


SortNumber
of stems
per plant
Relative yields
Probstier Group:—
Gold Rain2.07High yielder
Victory2.72
Hvitling2.3Lower yielder
White Probstier2.13
No.01272.42
Lines out of Back Tartarian:—
No. 02012
No. 02021.78Relatively low yielders and light stoolers
No. 02041.93
No. 02291.75
From natural crossing between
Black Tartarian and Probstier:—
No. 04952.41
No. 04962.08
No. 04971.96
No. 04992.91Best yielder and heaviest stooler
of this group at the Ultuna Station.
Lines out of Black Swedish oat:―
Fyris2.86Best yielder in this group
No. 010263.07
No. ―4.00
No. 010622.61
No. ―3.37
No. 0275 (Nigger)3.83Heavy stooler and poor yielder.
No. 0202 (Black Tart.)1.78Very light stooler and poor yielder

The above data clearly indicate that while rather marked differences can often be detected in oats in respect of their tendency to stool, yet it is quite unsafe to accept ‘stooling propensity’ as a basis of sort valuation.

In 1904 Vestergaard (80 p. 107) studied 67 different strains of barley representing in all about 20,000 plants, each of which was grown on from two to three different plots. This material was divided into four different classes according to yield and the following data obtained:—
ClassNumber
of
strains
Comparative
yield
Number
of head-
bearing
straws
per
plant
Per cent
head-
bearing
straws
per
plant
Length
of
straw
(c. m.)
Grain.
Per cent
of total
crop
Number
of head-
bearing
straws
per
16 sq. ft.
1171002.1374.692.948.71038
217962.0774.193.347.9981
317951.9772.293.947.7952
416871.9669.095.846.7929

From the above table it will be seen that contrary to the theory of Schribaux, the most productive strains have in this case at least the greatest number of head-bearing straws per plant, and a considerably smaller number of sterile or non head-bearing shoots. The best strains have also shorter and finer stems and produce a higher proportion of grain to straw.  They are thus less striking than those which proved actually less productive.  Further evidence is thus provided regarding the uncertain relationship existing between morphological characters and the real worth of a given sort.  Of greater importance is thickness of stand, even development of stolons and heads or panicles and the general appearance of the crop as regards vigor and freedom from disease.

The above investigations seem to indicate clearly that the practical value of a sort cannot be judged indirectly by means of botanical marks or morphological characters with any degree of certainty or reliability. Neither can so-called “ideal” plants be located with assurance in a mixed population on this basis. To quote Nilsson-Ehle (45, p. 311), “the great difficulty in breeding is to decide whether or not a form constitutes an advance.  That this can be decided only in a purely empirical way, through long continued practical experiments is essentially what makes breeding work so long.”

These conclusions served to introduce a second method of applying the pedigree system at Svalöf. Thus instead of basing the isolation of superior individuals purely upon botanical or morphological characters as was formerly the case, the principle has become to select a large number of individuals without special regard to such characters. The valuation of these individuals in so far as yield is concerned, rests upon yielding tests conducted with the greatest possible care over a series of years.

In order that this direct judgment might be more effective and more quickly accomplished local sort trials and special forms of comparative tests have been introduced. This change in method has naturally rendered breeding work much more difficult and exacting, especially where yield is the chief consideration. The alacrity and assurance with which an individual or sort was formerly rejected when failing to measure up to certain ideals in regard to visible characters, is no longer regarded justifiable, but instead extreme caution is observed lest unsuspected values be overlooked or lightly cast aside.

IV.—THE COMPOSITION OF A RACE OF CEREALS AND ITS VARIABILITY

Biotypes and Elementary species
From the evidence adduced thus far it seems clear that at least some of our common cultivated varieties contain a larger or smaller number of distinct hereditary types which, on being propagated separately, breed true.  Johannsen, as already indicated, has given to these entities the name Biotypes, the progeny of which he calls a “pure line.” Such bio-types, together with other intra-specific forms, are commonly spoken of by DeVries, as “elementary species.” In self-fertilizing plants such as wheat, oats and barley, pure lines may correctly be called strains, although this term is not always restricted to absolutely pure sorts. In this paper strain will be used to indicate pure lines only.

The presence of different types within a variety was formerly regarded as a manifestation of some inherent (hereditary) variation, a phenomenon which was believed to be continuous. Experience in the separate culture of these types, however, has shown them to be constant and distinct entities representing probably the smallest systematic division into which plant life can be divided.

Multiformity of Probstier oats
One of the most composite varieties of agricultural plants investigated thus far at Svalöf is the variety of white oats commonly grown in the Baltic region and known under different names of which Probstier is the most common.

In commenting upon the mixed character of this variety, Nilsson-Ehle (42, p. 125) says: “The multiplicity of forms found within this old unselected race is so great that it is difficult to obtain two individuals which will give identical progeny.” The respective progeny of these forms were distinguished by differences in degree of awn-development, hairiness of callus, size, form and color of kernels, average height of straw, width of leaf, etc.

Inability to distinguish all biotypes on the basis of outward appearance
The fact that two apparently identical plants in an old race may, when cultivated separately, prove to be quite distinct bio-types each producing its own peculiar progeny, served to show the need of submitting old varieties to an actual biological analysis. This analysis it was seen, could not be restricted to forms which simply appeared different, but must rather embrace a large number of individuals without special regard as to whether these differed in outward appearance or not.

This is the principle which has been followed by the above author in connection with the extensive analysis to which he has subjected the old Probstier variety during the past ten years. The results of one of these lines of studies may here be given: In 1906 there were sown out 72 small plots, each with seed from a single plant taken at random from a variety belonging to the Probstier group. The following table gives the analysis of each of these plots (42, p. 118):—
No.
of
plot
Color
of
kernel
Frequency
of
awns
(%)
Character
of
awns
Hairiness
of
callus
Average
length
of
kernels
(m.m.)
Average
width
of
kernels
(m.m.)
Weight
per
100
primary
kernels
(Grams)
Notes on other characters
1white0..116.02.994.08
22..117.12.974.09Weak strawed
341115.33.184.01
41-2015.53.083.98
551016.73.124.30Spikelets often 3-kernelled; plants broad-leaved.
671116.23.013.91
7111215.23.103.96Stiff strawed
8111116.92.993.86Spikelet often 3-kernelled
9111215.03.033.81
10121115.42.893.69Spikelet often 1-kernelled; plants short strawed
1112 1216.1 3.10 4.14Tall
1217 1 0 17.0 3.14 4.46
13 17 1 0 15.9 3.10 4.09
14 19 3 0 16.8 3.08 4.21
15 22 1 0 16.4 2.89 3.81Tall
16 22 4 0 15.3 3.08 4.10Early shooting of panicle
17 25 1 2 16.2 2.83 3.57
18 25 1 1 15.5 2.91 3.71
19 25 2 2 16.2 2.89 3.87Tall
20 26 2 0 15.2 3.22 4.08Short
21 26 1 1 16.2 3.10 4.20
22 28 2 0 16.9 3.12 4.32
23 34 1 2 16.6 2.91 3.76
24 41 2 1 16.9 3.16 4.40Spikelets often 3-kernelled; panicle one-sided.
25 42 1-2 0 16.9 2.95 4.00Spikelets often 3-kernelled
26 43 1 2 16.8 2.93 3.94
27 452 0 16.5 2.893.85
28 47 3216.93.064.07
29 48 3116.1 3.08 3.98Late shooting of panicle.
30 48 2 0 17.0 2.97 4.22Weak strawed
31 50 2 1 16.4 3.03 3.87
32 50 2 2 16.3 2.97 3.89Early shooting of panicle
33 50 3 0 17.8 2.95 4.09Spikelet often 3-kernelled
34 54 3216.4 2.97 4.17
35 60 1 0 17.0 2.93 3.92
36 62 2 0 16.6 2.99 4.08
37 63 1-2 0 16.4 3.01 4.23Short, stiff strawed
38 64 4 2 14.9 3.26 4.47
39 69 2214.9 2.97 3.82Tall, broad leaved
40 69 4 215.1 3.03 3.81Tall
41 70 5017.1 2.85 3.93
42 71 2 1 16.1 2.93 3.69Short, late shooting of panicle
43 71 3 2 17.6 2.89 3.85Spikelet often 3-kernelled, tall, panicle almost plume-like
44 74 3 0 15.4 2.97 4.09
45 77 2 2 17.4 2.97 4.04Spikelet often 3-kernelled
46 79 2-3 0 17.0 3.08 4.19Tall
47 79 2-3 2 17.1 3.03 4.17Weak-strawed, late shooting of panicle
48 80 2 2 16.5 2.93 3.90
49 84 3 1 16.1 3.14 4.34
50 85 2 2 17.4 3.06 4.09Spikelets often 3-kernelled; plants short strawed
51 85 2-3 2 16.9 3.03 4.01
52 85 2 0 15.6 2.99 4.02
53 87 2 2 16.4 2.91 3.78
54 89 2 2 15.8 2.99 3.89Late shooting of panicle
55 89 5 0 18.6 2.97 4.19Spikelets often 3-kernelled
56 91 4 2 18.2 3.01 4.50Spikelets often 3-kernelled
57 95 4 0 16.4 2.99 4.28
58 98 2 1 17.9 3.14 4.55Spikelets often 3-kernelled
59yellow0..217.02.893.70
60 1 1 1 16.7 3.12 4.20
61 1 1 2 16.9 2.89 3.88Tall
62 2 .. 0 15.5 2.99 3.64Short
63 4 1-2 1 16.5 2.81 3.62
64 5 2 1 16.8 2.81 3.49Spikelets often 3-kernelled
65 5 1 0 15.7 2.99 3.86Tall
66 15 1 0 16.4 2.93 3.79
67 17 2 2 16.5 2.85 3.67
68 17 1 1 16.6 2.87 3.61
69 23 4 2 16.7 3.12 4.18
70. 232 2 17.3 2.95 3.90Spikelets often 3-kernelled
71.2016.8 3.064.30Weak-strawed
72yellow 271-2116.32.913.89Short

It is worthy of notice here that the various characters by which the 72 strains considered in the above table are distinguished, group themselves around an average or “mean” according to the law of Quetelet, that is, the greatest number are found to possess the average condition of a given character. This may be illustrated by taking the average length and weight respectively, of the primary kernels of each strain thus:

Number of strains having length of kernel
indicated in opposite column
Average length of kernel of each strain in millimetres
214 to 15
1615 to 16
3816 to 17
1417 to 18
218 to 19
72 strains

Number of strains having weight per 100
kernels indicated in opposite column
Average weight of 100 kernels in each
strain. (Grams.)
23.4 to 3.6
113.6 to 3.8
233.8 to 4.0
214.0 to 4.2
104.2 to 4.4
54.4 to 4.6
72 strains


The situation indicated in the preceding tables may be expressed in still another manner.  Let us consider the second table in which the weight is given. It was found in this case that the weights of 100 kernels from the different strains fell into classes as follows:

Weight in Grams3.4 to 3.63.6 to 3.83.8 to 44 to 4.24.2 to 4.44.4 to 4.6
Frequency2112321105

   The classified data may be arranged graphically, in the following manner, to show what the Biometricians call “the frequency curve of variation in the weight of kernels”:—

Fig. VIII.—Frequency curve of variation in weight of kernels from different pure cultures
(Author del.)

The different types in the large table shown above are arranged according to the per cent of plants in each which developed awns. This, it will be noticed, varied from 0 to 989, in the white kernelled sort and from 0 to 279, in the yellow. The character of the awns (finer or rougher) is measured by the eye, (1) indicating a fine, weakly developed awn and (5) an awn which is strong and twisted.

The hairiness of the callus is also measured by the eye, (0) indicating absence of hair, (1) slightly hairy and (2) heavily haired.

The above analysis shows that scarcely any of the 72 plots produced identical progeny but rather are they regarded as distinct hereditary types which in respect to certain characters present a whole line of hereditary gradations from one extreme to another.

A point of prime importance revealed by these investigations is the independent nature of different characters. Thus the development of awns is quite independent of the development of hair on the callus; the length of the kernel is in no way governed by its breadth: low growing forms as well as high may have broad leaves or narrow leaves or they may have a stiff-branched panicle or a panicle which is more lax and drooping etc.  Each biotype in fact represents a definite combination of characters. Those familiar with the law of Mendel may find in this fact, further support for the conception that these forms have arisen through natural crossing.

Interesting observations regarding the variability and multiformity of distinct hereditary types found within this same variety of oats (Probstier) as well as in Squarehead wheat and Two-rowed barley have been recorded by Vestergaard of Denmark (80 p. 77-119). In Squarehead Wheat he distinguishes ten distinct biotypes on the basis of form of head. Although this variety is normally smooth chaffed he has found forms with velvet chaff which he believes to have originated from the genuine squarehead type.  Bearded heads have also been found although Squarehead is a bald wheat.  Certain cultures were further found to represent distinct biotypes on account of differences in size, form or color of leaves, although no marked differences in the head could be noted. Many cultures were readily distinguished on the basis of form, size and color of kernel and the degree of susceptibility to disease by which each was characterized.

In Denmark the most commonly cultivated two-rowed barleys are the so-called Danish Native barley, Chevalier barley and Prentice barley. Of the latter Vestergaard has cultivated about 400 separate cultures, a number of which have shown themselves to be distinct biotypes, although as a whole this variety has proven much less composite in character than has the common Danish barley. Reference has already been made in another connection (See p. 39) to the groups of distinct forms which have been taken out of this variety and specially investigated.

In view of the independent nature of the different characters which go to make up the individual it is possible for these to group themselves into every conceivable combination by cross-fertilization, artificial or by natural. That such grouping actually takes place seems to have been shown conclusively by the enormous amount of work in artificial hybridization which has been prosecuted with all kinds of Agricultural plants during the past ten years. It seems natural to suppose therefore that at least the great majority of the different strains or biotypes found within the old Probstier and other races and which represent different combinations have arisen by natural crossing. That natural crossing between sorts, even in such self-crossing in fertilizing genera as those to which wheat, oats and barley belong may occasionally take place has been clearly pointed out by such recognized authorities as Rimpau (60), Kornicke (20), Kiessling (19 p. 73), Nilsson-Ehle (49 p. 15) and Tedin (71 p. 119).

The multitude of distinct hereditary combinations which may arise through a relatively small number of independent differentiating units was pointed out by Mendel who showed that only 10 such units are necessary to make possible as many as 1,024 different constant (homozygous) combinations. Since it is easily within the range of two hereditary types to differ in as many as 10 different characters it is only necessary that these become crossed in order to produce a multiformity of combinations corresponding exactly with that which is represented in an old mixed variety.

The progeny of a crossing are of course hybrids and according to the law of Mendel, a certain proportion of these become practically constant in succeeding generations. Others segregate or divide producing constant (homozygous) and inconstant (heterozygous) combinations. The latter continue to segregate until so reduced in proportion to the constant forms as to finally become practically lost sight of in the case of normal self-fertilizers. Thus in the end are to be found a whole host of constant combinations each of which, further crossing excluded, breeds true in succeeding generations.

The constancy of pure lines in self fertilizing species of plants seems to displace at one stroke practically all previous conceptions regarding the question of variation. We must abandon the idea that all life is in a constant state of unrest, always varying this way or that. “Had this analytical principle” says Johannsen, “been used in the times of Darwin or had it even been appreciated by the Biometrician school certainly the real bearing of selection might long since have been rightly understood” (18 p. 143).

By reason of the variability of soil, moisture, light and other external factors there are always to be found a larger or smaller number of individuals and within a pure line which deviate from the common type.  There are also to be found variations between certain parts of individuals. The first form of variation can best be designated as individual variation (modification), and the latter as partial modification. Neither, however, is regarded as hereditary.  These modifications may be sufficient to cause certain individuals, within a given strain to “transgress” or “over-lap” those in another. Thus a plant belonging to a certain strain may become so altered by external conditions as to become apparently identical with that belonging to another. An excellent example is afforded in connection with the various strains taken out of the Probstier oats. The length of each individual in six of these strains is indicated in the following diagram (42, p. 128);—

Length of straw in
centimetres
95100105110115120125130135140145150155
Six strains from
Probstier Oats
1358751..
..1191217721..
11134813822..
..138131572..
..226713185..
..1..69198
[Totals]2572126403632172327248

A study of the above diagram clearly indicates that a direct botanical examination of a common population can give scarcely more than an indication of its constitutents [sic]. Only by the separate culture of a sufficient number of individuals and by a determination of the average condition of each character in the progeny can an effective analysis be made. It is this average condition which distinguishes one strain from all others. This fact constitutes a second great reason why the isolation of superior mother plants as starting points for new races cannot depend exclusively upon apparent morphological differences.

   In commenting upon the influence of mass-selection, in a case such as this, Nilsson-Ehle (42 p. 128) says: “Were a mass-selection of plants over 125 c.m. in height to be made from this old mixed sort, plants from types which normally produce a short straw would be taken as would also those from types which normally produce a taller growth. The latter would naturally preponderate whereby a certain advance in the desired direction would likely be made.”  It is quite possible, however, that an advance in one direction may be made at the expense of some more valuable quality, hence the _danger which is associated with this form of selection.

The Origin of Aberrant Forms as Quantitative Hereditary Variations.

Apart from the mass of apparently related individuals which go to make up the greater part of a plant population, there may occasionally arise strange forms which at first sight do not seem traceable to any definite parentage. There may arise bearded heads of wheat in a bald sort, brown-chaffed individuals in a white-chaffed sort, white-kernelled forms in a red-kernelled sort, etc. In oats, white and grey kernelled individuals have been found in black-grained sorts and vice versa, while side oat types have been found in sorts characterized by spreading panicles. Formerly these aberrant forms were commonly regarded as Atavists or Reversions, being looked upon as the sudden reappearance of certain ancestral characters. More recently they have received the name Mutation. Experience at Svalöf and elsewhere has shown that the majority of these so-called novelties which thus suddenly appear in cultivated crops may be produced artificially by cross-hybridization and may therefore be regarded in most cases, simply as new combinations of already existing units. Apart from the great scientific interest which surrounds the appearance of these aberrant individuals there is an interest for the practical breeder which cannot be denied. If these forms represent mutations by which apparently new characters are suddenly acquired, it would clearly be the breeder’s main duty to watch carefully for their appearance in his fields with a view to isolating and propagating them and perchance obtaining something better than the old sort. On the other hand, if they represent the results of natural crossings between different sorts, as they are now believed to do, it is of much less importance to spend time in seeking for things which can be produced artificially with much greater assurance of obtaining an advance. Thus where formerly, striking natural crosses found in the experimental plots at Svalöf were eagerly isolated and studied they are now very largely ignored unless the marks by which they are characterized point to a certain parentage of known value. Instead it is preferred to make crossings artificially between known sorts whose values have already been proven.

An explanation of the origin of new combinations is afforded by Mendel’s Law of Hybrids. In fact, this law is now the basis of practically all investigation in the realm of hybridism and should be understood by all breeders.  Before the law of Mendel became known cross-fertilization was looked upon as a means of stimulating or creating variation, making the selection of superior variants possible. The varieties or sorts used for this purpose was not a matter of great concern as almost any two, it was thought, were capable of producing, when crossed, variations which might form the basis of new and better sorts. When Mendel’s law became better understood, crossing came to be regarded not as a means of inducing variation, but as a means of combining already existing units, allowing certain characters of one parent to be combined with those of another.

One of the requisites for the application of this law is that the two parents possess characters which are opposed to each other. As examples may be cited the simple characters, Baldness and Beardedness in wheat, Roundness and Wrinkledness in pease, Smoothness and Hairiness of wheat chaff, etc. These two opposing characters in each case are termed a “character pair.” When one of the characters belonging to a certain pair js “stronger” than the other it is said to-be Dominant. In this case only this character will appear in the first generation hybrids, the other remaining recessive or concealed. In wheats, Baldness is dominant over Beardedness. The first generation from a crossing between a Bald and a Bearded sort will therefore be Bald, but in the second generation there will again be found both bald and bearded forms. Mendel showed that where simple characters, such as those now under consideration, are involved, the individuals in the second generation fall unto two main groups, one group representing the character of the recessive parent and the other similar to or approximating the dominant one.  Those resembling the former parent represent about 25%, of the whole number. These breed true in succeeding generations. Of the second group, which represents 75% of the whole, ⅓ will produce true dominants while the remaining ⅔ will again divide or segregate in the next generation producing the same constant and inconstant forms. This fact of segregation is one of the essential discoveries in Mendel’s law.

The proportions which are obtained when two sorts possessing simple alterating characters are crossed (monohybrid combination) may be represented as follows:—


It will be seen from the above that the inconstant Bald forms segregate in each generation into 75% Bald and 25%, Bearded, or in the proportions 3:1.

Mendel has given a simple and interesting explanation of his famous law, a knowledge of which is essential to a proper understanding of the work at Svalöf, as indeed of that at most other breeding centres of the present day. This explanation may be presented substantially as follows:—
   In the higher plants and animals reproduction takes place as a result of a union between two: sexual cells (gametes), viz.—a male and female cell. Each gamete which is concerned in the origin of a given variety or species possesses a definite factor for each of the characters by which such variety or species is distinguished. Thus in the case of a red flowered variety of plant, the gametes which are responsible for its being, possessed a factor for red color. Similarly, a constant tall sort has a gamete with the factor for tallness. A low growing form has a gamete with the factor for low growth, etc. Now when a crossing is effected between say a black-kernelled and a white-kernelled sort, a “black” gamete unites with a “white” gamete with the result that a hybrid is produced which is black or dark brownish. This is due to the fact that “black” is dominant over “white.” When this dark hybrid individual itself develops gametes, these do not possess the factor for black or brown only, but rather a certain proportion of them possess the factor for black and a certain proportion the factor for white.

This segregation, or division, concerns both the female cell (egg-cell) and the male cell (sperm cell) so that 50%, of each kind of cell possess the factor for black and the other 50%, the factor for white.

When fertilization takes place between the gametes (egg and sperm cells) of the same plant, as they usually do in self-fertilizating species, there are four different combinations possible, thus:

Eqg-cellSperm-cellProgeny
1.BlackXBlackBlack
2.BlackXWhiteBrown
3.WhiteXBlackBrown
4.WhiteXWhiteWhite

From the above it will be seen that should all possible combinations be effected and should the black and white gametes be present in like numbers the progeny (second generation, F2) shall consist of individuals ¼ of which are black, ½ brown and ¼ white. If the black and brown are thrown together into a single group there will be established the proportions 3 black-brown; 1 white.

Nilsson-Ehle (56 p. 6) explains the above principle in the following graphical manner:—

FIG. IX.—Graphic explanation of the Law of Mendel.

Those individuals belonging to the progeny of the above hybrid which have originated as a result of a union of two black or two white gametes (homozygotic individuals) can produce only black and white gametes respectively, and their progeny in each case will be constant in succeeding generations. Those individuals on the other hand, which have been produced by the union of unlike gametes (heterozygotic individuals) such as black and white, for example, will in turn produce both black and white gametes and the progeny will therefore display the same “variation” as that shown in the original crossing.

When more than one character pair is involved the result is somewhat more complicated yet in full accord with the leading principle. If, for example, a Bald Lax-eared wheat is crossed with a Bearded Dense eared sort (dihybrid combination,) there are two character pairs to be dealt with, instead of one. These may be represented as follows:—

Biffen (8) has shown that the first generation hybrids (F1) from crosses between sorts having the above characters differ according to the varieties used. They are Bald or nearly so and lax-eared or strongly inclined in this direction. Baldness and Laxness are here the dominant characters and hence only Bald and Lax-eared forms appear in the first generation. In the second generation hybrids there will be shown different combinations of the potentialities of the parents arising through a union of egg-cells and pollen-cells.  Considering the two character pairs in question there may be four kinds of egg-cells involved in the union, namely egg cells combining the potentialities of Bald and lax-eared types, Bald and dense eared types, Bearded and dense-eared and Bearded and lax-eared. The same combinations are possible in the formation of the sperm or pollen cell. When these four kinds of egg-cells and four kinds of pollen cells are brought together, 16 combinations are possible. These maybe shown in the following manner allowing B to represent the Bald character, b the bearded, L the lax and l the dense: (F2=second generation; F3=third generation or progeny of F2).

Description of progeny of F2
B LXB L=Bald and Lax forms
B LXB l=Bald and Lax (+ dense)
B LXb L=Bald and “ (+ bearded)
B LXb l=Bald and “ (+ bearded and dense)
B lXB L=Bald and Lax (+ dense)
B lXB l=Bald and dense
B lXb L=Bald and Lax (+ dense and bearded)
B lXb l=Bald and dense (+ bearded)
b LXB L=Bald and Lax (+ bearded)
b LXB l=Bald and Lax (+ bearded and dense)
b LXb L=Bearded and Lax
b LXb l=Bearded and Lax (+ dense)
b lXB L=Bald and Lax (+ bearded and dense)
b lXB l=Bald and dense (+ bearded)
b lXb L=Bearded and Lax (+ dense)
b lXb l=Bearded and dense

Without regard to whether the above combinations are constant or inconstant we find 9 which have both of the Dominant characters, viz.: Baldness and Laxness, 3 and 3 with either of the Dominants and either of the Recessives and 1 with both Recessives, making in all the 16 combinations indicated.  These combinations and proportions may be expressed concisely as follows:—

9 BL + 3 Bl + 3 bL +1 bl = 16.

These are the normal combinations and proportions which may be expected in an ordinary dihybrid crossing when simple alternating characters are involved.

That the segregation of the progeny in the second generation of dihybrid crossings actually takes place in the above manner and gives results which correspond very closely with what might be theoretically expected has been shown by numerous investigators working in widely different fields. A good example is afforded by Tedin (72, p. 158) in crossings with pease. In two of the sorts the two dominant characters were red color of flower and black hilum, while the two recessive characters were white flower and light colored hilum. In a third crossing the two dominant characters were yellowness and roundness of seeds, while the recessive characters were greenness and angularity of seeds. The characters of the parents together with the actual combinations and proportions into which the second generation divided themselves is shown as follows:—

Characters of Parents
Dominant CharactersRecessive Characters
Crossing Nos.
I. & II
{A (Red flowers)a (white flowers)
B (Black hilum)b (light hilum)
Crossing No.
III
{A (Yellow seed)a (green seed)
B (Round seed)b (angular seed)

VISIBLE CHARACTERS SHOWN IN SECOND GENERATION HYBRIDS
A BAba Bab
Crossing No.
I
{Number221:78:71:25
Relation93.22.91
Crossing No.
II
{Number250:87:82:33
Relation33.13.01.2
Crossing No.
III
{Number1342:445:513:168
Relation93.03.41.1

The above proportions, it will be noted, correspond very closely with what might be theoretically expected, viz., the proportions 9 : 3 : 3 : 1.

As has already been pointed out in this paper, the number of possible combinations is increased immensely, the greater the number of differentiating characters involved in the crossing. The proportions, in normal cases at least, agree with the same law as that which governs the union in monohybrid and dihybrid combinations.

From the above elucidation of the Law of Mendel there emerges the two essential discoveries of that law, one of which indeed may be said to be complementary of the other. These are as follow:—
    (a) The different characters behave as units and, during the process of reproduction, segregate and are carried over from one generation to another without undergoing any essential change.
    (b) The different characters act independently of each other by reason of which fact many different combinations may be effected by different groupings of a relatively small number of units.

Thus has the Mendelian annunciation thrown an entirely new light on the nature of hereditary variations and has introduced quite a new principle into biological science.

In establishing his law of hybrids, Mendel wisely enough worked with simple differentiating characters, and it was upon the behaviour of these that he framed his law. At the same time he premised that complications would doubtless occur which would require a further exploitation of the principles involved to explain. These complications have come and have been met by various workers. To some they have been discouraging and confusing; to others they have served as a stimulant to further investigation and study. Crossing work in great extension has therefore been prosecuted and the progeny studied with extreme care. In this way the unit constitution of many sorts used as parents has been determined. This knowledge has served not only to elucidate some of the apparent irregularities in, or exceptions to, the Mendelian annunciation, but also seems to offer an explanation of the appearance of many of the strange forms in our cultivated crops which indeed is our chief concern just now.

A direct outcome of these investigations has been the establishing of two new theories which may be regarded simply as further developments or modifications of the Law of Mendel, as that law was first described. The law itself is in no way altered by these developments; it is only shown to be applicable to complex as well as to simple problems. The first of these theories is known as the Theory of Presence and Absence and implies that of “Presence the “Presence” of a certain unit or character with its corresponding “Absence ” together form, paradoxical though it may seem, a character pair. This idea was first applied to plant life by Correns as a result of many years of most exacting work, although Bateson, Punnett and E. R. Saunders were the first to fully recognize the principle and to develop it as a new and consistent theory.

This theory will be better understood when we remember that Mendel considered there to be in the gamete a definite something corresponding to the dominant character or a definite something corresponding to the recessive character. In no case, however, could these coexist in a single gamete.  For these somethings the term Factor has come to be commonly used.

Mendel believed that the gamete always carried a definite factor corresponding to either the dominant character or the recessive character of a character-pair. No gamete however, could carry more than one of the two factors belonging to such a pair, by reason of which fact the characters were said to be alternative to each other. This conception has undergone a slight modification within recent years owing to the number of cases which it was unable to explain. This difficulty was met in a simple way by the theory of Presence and Absence.

Some excellent illustrations of the manner in which this theory may be applied, together with the difficulties which it seems to elucidate, are afforded by Nilsson-Ehle in crossings between different sorts of oats and wheat. Thus in crossings between certain black and yellow-grained oat sorts, white-kernelled individuals appeared regularly in the second generation. According to ideas which prevailed before exact experimental data were available, these white grained forms would be regarded either as ‘reversions’ to the character of a former parent, to the sudden reappearance of a previously latent character or perhaps to something quite new. Not only did new forms arise in these crossings but the proportions into which the hybrids grouped themselves showed that the combination was not a simple monohybrid one.

A concrete example is afforded in the crossing made at Svalöf between the yellow-grained oat sort No. 0375 and the Black sort No. 0401 (49 p. 44). In the second generation there were found in one case 155 Black grained plants, 43 yellow-yellowish and 15 white or in the proportion of 10.3 black; 2.9 yellow-yellowish; 1 white. By grouping the yellow and white grained forms together we have the proportions 2.7 black; 1 yellow-white. .Of the above 213 plants, 185 were reasonably well developed. When the seed of the latter came to be sown out in separate plots there were obtained the following:—
     45 plots produced constant black-kernelled plants.
     20 "  showed a mixture of black and yellow kernelled plants.
     43 "   showed a mixture of black, yellow and white kernelled plants.
     23 “ showed a mixture of black and white kernelled plants.
     16 “ produced constant yellow-kernelled plants.
     23 “ showed a mixture of yellow and white kernelled plants.
     15 “ produced constant white-kernelled plants.
     185 "

The crossing in question was therefore clearly enough a dihybrid one, since some plots contained only black and white-kernelled forms and others only black and yellow.

   In the light of the Theory of Presence and Absence this strange phenomenon seems easy of explanation. Instead of Black and Yellow forming a single character-pair each of these acts independently of the other, Black with the absence of black forming one pair and Yellow with the absence of yellow forming the second pair. This crossing may be illustrated as follows:—

“On this theory,” says Punnett (55 p. 35) “the dominant character of an alternative pair owes its dominance to the presence of a factor, which is absent in the recessive.”

The Black oat is therefore black owing to the fact that it possesses a factor for “blackness” which is absent in the recessive. Instead of the gamete always carrying a definite factor for either dominance or recessiveness it may be regarded as either possessing or not possessing one of the factors of an alternative pair; in other words the factor is either Present or Absent. This conception will become clearer if we follow its application in detail to the case of the above crossing. In this case the presence of each of the two factors Black (B) and Yellow (Y) is alternative to its respective absence.  The Black-grained oat contains a factor for Black but not a factor for yellow, while in a similar manner the Yellow-grained oat contains the factor for yellow but not that for Black. In the above scheme the absence of Black and Yellow has been indicated by a small “b” and “y” respectively for the sake of convenience.

As already indicated (See page 54) when two character pairs are involved in a crossing as in the above case, there may arise in the hybrids four kinds of egg-cells and four kinds of pollen cells. Either the egg-cells or pollen cells may be represented as follows:—BY, By, bY, by. If the four different, kinds of egg-cells unite in all possible ways with the four different kinds of pollen cells involved in the above crossing sixteen different combinations are possible. These may be represented symbolically as follow:—

F2F3
BYXBY=Black (+ Yellow but yellow hidden)Constant B
BYXBy=Black (+ yellowish)Constant B
BYXbY=Black (+ yellow)3 B : 1 y
BYXby=Black (+ yellowish)12 B:3 y:1 w
ByXBY=Black (+ yellowish)Constant B
ByXBy=Black (pure)Constant B
ByXbY=Black (+ yellow)12 B : 3 y : 1 w
ByXby=Black3 B : 1 w
bYXBY=Black (+ yellow)3 B : 1 w
bYXBy=Black (+ yellowish)12 B:3 y:1 w
bYXbY=YellowConstant Y
bYXby=Yellowish3 Y : 1 w
byXBY=Black (+ yellowish)12 B:3 y:1 w
byXBy=Black3 B : 1 w
byXbY=Yellowish3 Y : 1 w
byXby=WhiteConstant W
F2: 12 B; 3 Y.—Yellowish; 1 white.

Twelve out of the 16 zygotes contain “B” but not “Y” and are thus pure Blacks. Three contain “Y” but not “B” and are thus pure Yellow.  Nine contain “B” and “Y,” but since “B” is dominant over “Y” they are all Black or Blackish. Finally one contains neither Black nor Yellow, and is White. The above scheme illustrates clearly the manner in which new and strange forms may arise either under domestication or in nature.

When the white-kernelled sort No. 0315 was crossed with the Black Moss variety (No. 0670), there were obtained not only Blacks and Whites but Greys as well. The proportions obtained moreover corresponded with those peculiar to a dihybrid combination. The actual proportion in this case was 187 black, 38 grey and 17 white, or 11 black, 2.2 grey, 1 white (49, p. 25).  The assumption here is that this particular sort possesses not only a unit for Black color but also a unit for grey, although the grey is hidden until brought into certain combinations when it appears as a new character. The following dihybrid scheme is submitted as explaining the situation:—

Here we have represented four possible combinations which may go to form four different kinds of pollen cells and four of egg-cells, viz.: b G, b g, B G, Bg.  When these four kinds of pollen cells and four kinds of egg-cells are brought together the sixteen combinations peculiar to a dihybrid crossing are made, the combinations b G X b G, b G X bg and bg X b G representing the “new” grey forms.

When the black sort Moss (0670) which, as we have seen, apparently possessed a unit for Grey as well as a unit for Black, was crossed with the yellow sort Gold Rain (0386) there were obtained in the second generation, Blacks, Yellows, Greys and Whites, the two latter representing apparently quite new forms (49, p. 48). The proportions of the different forms of hybrids obtained showed furthermore, that the crossing had been a trihybrid one that is, three character pairs had been involved. These may be represented in the following scheme:—

Gold RainMoss
b(absence of black)B(Black)
g(absence of grey)G(Grey)
Y(Yellow)y(absence of yellow)

The gametes (sexual cells) formed in this case are of eight kinds, viz.:
BGY, BGy, BgY, bGY, Bgy, bGY, bgY, bgy.

In the second generation the progeny of four individual plants from F1 were grown in separate cultures and gave the following results:—

(a)F2116Black,22Grey,5yellow-yellowish,2Grey and yellow,10White
(b)F254Black,11Grey,9yellow-yellowish,2Grey and yellow,3White
(c)F229Black,6Grey,3yellow-yellowish,0Grey and yellow,4White
(d)F259Black,14Grey,3yellow-yellowish,1Grey and yellow,5White
Total:  258Black,53Grey,20yellow-yellowish,5Grey and yellow,22White

The second theory, or modification of the Mendelian theory, to which reference has already been made as seeming to contribute to a better understanding of the origin of hereditary gradations and to the occurrence of aberrant types, has been advanced by Nilsson-Ehle (46 and 49) in connection with work with cereal grains, and by East (11) of the United States of America, with Maize. This theory assumes that a certain character may consist of more than one unit, each unit having practically the same external effect.  Thus it has been observed that a black-kernelled oat sort may possess more than one unit for Black, each unit alone being able to produce the typical black colour. A good example is afforded in the crossing between the black sort 0668 and Ligowo, 0353 (white). The former sort has been found on analysis to contain two independent units for Black (B1, B2) and also a unit for Grey (G), all of which are apparently absent in the sort 0353. The constitution of these sorts is represented in the following manner:—

0668B1B2G
0353b1b2g

This crossing is therefore a trihybrid one instead of the simple monohybrid, although the latter might reasonably be expected in the absence of any exact knowledge as to the inner constitution of the sorts involved.

FOOTNOTES

1.  By “Middle Sweden,” as used in this paper, is meant that part of Sweden lying between parallels of latitudes 58 and 60.
2.  Fruwirth.
3.  Bolin resigned his position at Svalöf in 1900, when Tedin took over the barley work in addition to that which he already had with peas and vetches.