VARIETAL IMPROVEMENT
IN HOPS

D. C. SMITH, Formerly Agent, Division of Drug and Related Plants, Bureau of Plant Industry1

[ABSTRACT.]  BEER, ale, and other malt beverages depend principally on hops for their characteristic flavors, and no satisfactory substitute has ever been found. Improvement of hops by breeding is, therefore, of vital concern to both brewers and growers. The attainment of a choice product is very difficult, since the hop plant is extremely sensitive to sun, wind, heat, rain, insects, and diseases, and the quality of the cone depends on type, color, soundness, aroma, and content of resins and essential oils. Breeding may play an important part in improving most of these characteristics. The varietal improvement program is new in the United States and though the hop plant is not easy to deal with, the progress made in developing superior varieties in Europe suggests what may be accomplished with sustained and active investigations.

LUPULIN, a substance consisting of resins and essential oil, imparts to beer, ale, and other malt beverages their characteristic bitter flavor. The scales or bracts of the hop—which resembles a fir cone in its general makeup—possess small, yellow, granular bodies or lupulin grains, easily visible to the eye (fig. 1). These contain the resins and oil. The oil, contributing also to the aroma, is usually driven off in the boiling process but may be replaced later. Materials known as tannins occurring in the scales and stem of the cone aid in the clarification of the brew after boiling.


Figure 1.—Branch of hop vine with mature, well-developed cone below and blighted, withered cones due to downy mildew above and to the side.

Each 31-gallon barrel of beer brewed in the United States requires only a half to four-fifths of a pound of hops, though abroad the figure sometimes reaches 1¼ pounds. Thus in spite of the extent of the brewing industry, the acreage of hops required is of minor importance agriculturally when compared with many crops. Hops are all- important to the brewers, however, since beer is made principally of malted barley, hops, and water. There are rather exacting require- ments in quality of hops, and both yield and quality are determined by many influences. Breeding of better hops, therefore, becomes an undertaking of vital concern both to brewers and to growers.

In other countries attention has been given to hop breeding as a means of improvement for many years. Such work with hops in the United States is at its beginning, though much progress has been made in recent years in breeding other crop plants. Some of the back-ground of hop culture will help the reader to better understand the breeder’s work.

USE OF HOPS ANCIENT IN ORIGIN

Just when hopped beer was first made is not known. The Egyptians had a sweet-sour alcoholic beverage made like beer but without hops. Hops were apparently used by the Greeks only as a salad plant; even today young hop shoots are eaten like asparagus by some people. In early times hops were supposed to free the blood of “all impurities; tumors, and flatulence”, cure the itch and other skin diseases, and “relieve the liver and spleen.” Taken as a fresh vegetable, they may well have had some beneficial effect in the diet. Today individuals may be found who believe that sleeping on a pillow stuffed with dried hops somehow contributes to health.

But the overwhelming utilization of hops has been in brewing, this use being first developed either in Russia or in Germany. German records go back to 768 A. D., in the time of Charlemagne, when King Pepin le Bref donated hop gardens to the monastery of St. Denis.  Subsequently many monasteries became famous for their brews. By 1320-30 A. D., hopped beer was in general favor in Germany. Hop culture spread to the Netherlands, and John the Bold, Duke of Burgundy, founded a Knightly Order of the Hop. Late in the fifteenth century the plant was introduced into England, but Henry VII and Henry VIII liked beer without hops and prohibited their use. Swedish tastes were the opposite; an ordinance of 1440 required every farmer to grow 40 poles of hops. In Bohemia the Emperor Charles IV personally selected the spots most suitable for hop growing.  Today leading producing countries abroad are England and Wales, Germany, Czechoslovakia, France, and Belgium.

In North America, hop growing began in New Netherlands as early as 1629 and in Virginia in 1648, though it did not become important until about 1800. In 1808 the first hop yard was established in New York. In 1849 the New England States and New York produced nearly 1,500,000 pounds, of which New York grew 70 percent. After the Civil War the industry developed in Wisconsin, reaching a maximum of 25,000 bales2 in 1869. In 1865, Oneida County, N. Y., produced 1,265,000 pounds, and in 1879 the State reached an all-time maximum of 21,629,000 pounds.3

The growing of hops on the Pacific coast was started between 1859 and 1869. Though New York was still the leading State in 1899, the production in Oregon and that in California each exceeded that of New York by 1909. In recent years hop cultivation in this country, except in Washington, Oregon, and California, has been negligible.

In 1935 these three States harvested 47,746,000 pounds of hops on 38,900 acres. Slightly over half of the tonnage was grown in Oregon.

During the twenties hop growing in New York was practically wiped out by powdery mildew, but there is a revival of interest in that State, as indicated by the work recently begun by the New York (State) Agricultural Experiment Station at Geneva looking toward the improvement of hop varieties.

The growing of hops is somewhat similar to that of pole beans.  The vines are trained on poles or pole-and-wire trellises, ordinarily 10 to 20 feet in height. Plants are spaced from 4 to 8 feet apart, the latter distance being most general on the Pacific coast. At harvest the vines are let down and the cones are picked by hand. The green hops are then hauled to drying houses, piled in bulk, and slowly dried with artificial heat for about 20 hours. Later they are compressed into bales of about 200 pounds each, sewn over with burlap, and the grower’s part is completed.

Hops are long-lived perennial plants propagated by root cuttings and having a strong climbing habit. Curiously enough, the vines always wind in the same direction. New shoots are produced each year, and after harvest old growth is removed as in the case of cane fruits. Plants may be grown from seed, but they then exhibit great diversity in characters, many being strikingly inferior. Few growers have noticed hop seeds germinate. Hop plants possess remarkable vigor, young vines having been observed, under favorable conditions, to elongate 12 inches in 24 hours.

Hops are closely allied only to elm, mulberry, hemp, and nettles among the commonly known plants and are known to botanists as Humulus lupulus L.  A native American type has been segregated as H. americanus Nutt. An annual ornamental variety called the Japanese hop (H. japonicus Sieb. and Zuce.) is a cousin, as is H. neomexicanus (A. Nels. and Cockerell) Rydb., a native sort found in Colorado and vicinity. The first two species mentioned include all commercial hop varieties.

PECULIARITIES AND PROBLEMS IN HOP BREEDING

THE HOP is one of the few cultivated plant species in which male and female flowers are borne on different individuals. Since commercial hops are the dried and pressed cones from the female plants and these develop without fertilization, the males are not indispensable in commercial culture. The latter do serve to stimulate production of larger, heavier, and earlier maturing cones by the female plants (20). Such hops contain seeds, which contribute to the weight but which have no value in brewing, and in parts of continental Europe the presence of male plants in yards is forbidden by law. In the United States and England about 1 male to 100 female plants may be grown.

To the breeder, seed production is necessary, since it is in seedling progenies that opportunity for selection of improved varieties is most promising. The breeding problem is closely analogous to that in dairy-cattle improvement. There is no method of determining the value of a sire in providing desirable heredity to obtain high-producing cows except by progeny tests, since milk production, like hop development, is a purely female character. Nevertheless, from a hereditary viewpoint, the male contributes markedly in each case.

BREWING REQUIREMENTS, YIELD, AND MATURITY

The characteristics of choice hops, from thé brewmasters’ viewpoint, are relatively few. They should possess a high soft-resin content, delicate aroma, and a clean, bright appearance, and contain few or no seeds, leaves, and stems. Because of the slow, gradual development and fragile nature of the cone, coupled with the extreme sensitivity of the plant to sun, wind, heat, rain, insects, and diseases, the attainment of a choice product is exceedingly difficult. Harvesting operations also play no small part in determining the quality of hops received by the brewery. Though much investigational work has been done in attempts to find suitable substitutes for hops, the use of this crop continues to be the only means in use of giving the desired qualities to beer.

In the culture of hops, the grower has many serious troubles. Most important among these are maintenance of yields, control of diseases and insects, standardization of high quality, and many minor difficulties arising from these. The first task of the breeder is to recognize and understand these factors.

The world over, yields of dry hops per acre may range from 300 to 4,000 pounds. While much depends on the country and locality, the variety used is of chief interest in this respect. The principal varieties of the Pacific coast are Late Clusters, comprising about 75 percent5 of the acreage; Fuggles, about 15 percent; and Early Clusters, 10 percent. In good years, Late Clusters produce an average of about 1,500 pounds, Early Clusters 1,300 pounds, and Fuggles 1,100 pounds of dry hops per acre. Incidentally, yields in continental Europe are usually from 600 to 1,100 pounds per acre while those of England and Wales approximate those of the United States.

Fuggles is the earliest maturing variety, usually being ready for harvest about August 20, with Early Clusters closely following.  Ripening of Late Clusters, which is the main crop, begins in Oregon in early September. Maturity of hops is generally earlier in California and to some extent in the Yakima Valley of Washington.  Harvesting of Late Clusters may extend into early October. Many growers have acreages of two or more varieties, which allows a longer harvesting season. Increased yields are always a breeder’s objective and the period of maturity is of importance in most sections.

DOWNY MILDEW, SCOURGE OF THE HOP PLANT

Like other plants, hops are attacked by various diseases, the most serious of which, at the present time, is downy mildew. Other important troubles in the United States are blue mold or powdery mildew, sooty mold, which accompanies infestations of plant lice, and crown gall. Blue mold, a serious disease in England and to some extent responsible for the decline of hop production in New York, has not been reported on the Pacific coast. Sooty mold may be serious in any year when plant lice are prevalent. These diseases may attack hop cones, leaves, roots, or stems causing lowered quality or complete destruction. The effects of downy mildew on cone development are shown in figure 1. In addition to those mentioned, other minor diseases of various types have often been present in Europe and the United States.

In recent years hop growers throughout the principal hop-growing countries have been greatly concerned with downy mildew. Its ravages have resembled in many respects those of the late blight disease of the potato, which caused the Irish famine in 1845 and 1846, or of the frequent stem rust epidemics of cereals in the Middle West.

Downy mildew was first described in Japan in 1905. In 1909 it was observed in the United States, being found in Wisconsin. In 1920 minor attacks of the disease were seen at Wye, in Kent, England, but in 1921 it was not observed there. During 1922 and 1923 it increased in prevalence at Wye, and in 1923 it was reported in Germany and Czechoslovakia. Belgium and France reported it in 1924 and the Union of Soviet Socialist Republics in 1925. In 1926 it appeared in Italy. Beginningin 1927 serious losses were caused, England suffer- ing damage estimated at nearly one-third of the crop and Bavaria also experiencing heavy losses. Some Bavarian growers sprayed 10 times during the season to control the spread of the trouble.  Since 1927 the disease has appeared irregularly in Europe, but in individual localities losses may involve the entire crop. Weather conditions are important influences in the development of the disease.

Though found in Wisconsin in 1915, downy mildew did not cause economic losses in North America until 1928, when it appeared in New York, Manitoba, and British Columbia. In 1929 it developed extensively in western Washington and in 1930 was severe in western Oregon. The disease did not appear in coastal California until 1934 and in the Sacramento Valley until 1935. During 1936 it was prevalent in all areas where it had been found previously and caused a marked reduction in the yield and quality of the crop. To date it has not been officially recorded as existing in the Yakima Valley of Washington, though experienced growers have reported traces of it.

While downy mildew appears irregularly, it has been estimated that 20 to 25 percent of the crop is annually lost through the depredations of this disease in the Pacific Coast States. The source of the organism causing downy mildew (Pseudopernospora humuli (Miyabe and Tak.) Wilson) is problematical, but it is thought to be native on wild hops in the United States. The control of this devastating disease is perhaps the most important concern of hop producers both in the United States and in Europe and is a major objective of the breeder.

QUALITY AND OTHER CONSIDERATIONS

Particularly in recent years, but more or less persistently over a long period, growers have been concerned with problems affecting quality. Considered from the variety-improvement viewpoint, items of importance are soft-resin content, aroma, and the existence of seeds. Commercially, hops are bought on the basis of general variety or type, color, aroma, lupulin content, and soundness. These might be termed "sight", “smell", and “touch” characters, and experienced growers and dealers rely greatly on these three senses. Recently resin content as determined by chemical analysis has become a greater influence in the hop trade.

Proper attention to the various steps in harvesting and curing favors quality to a large extent, but aside from this, variety and locality are also extremely significant factors. With respect to soft-resin content, American-grown hops are equal or superior to the best European lots. The latter are reputed to be preferable in aroma.  Continental hops are also noteworthy for their freedom from seeds as compared with the English and American products. German and Bohemian hops continue to sell at a high premium over domestic lots in the New York markets. Though sufficient domestic production of hops for supplying the American trade usually exists, the use of a certain percentage of foreign hops for brewing is a general practice in this country. To improve the quality of domestic hops is thus another primary object of breeding efforts.

Insects affecting hops most frequently are plant lice or aphids and the red spider. These pests exist in both European and Pacific coast hop sections. Root borers, cutworms, flea beetles, and other insects occasionally do considerable damage. Aphids have been generally present and, where they are numerous, the secretion of honeydew, a sticky sweet substance, reduces quality and serves as a substratum for molds to develop. Red spiders affect the foliage mainly and are usually prevalent under conditions of slow growth and dry, warm weather.

In picking, hops that separate readily from the vines are harvested with the least crumbling and breaking. Types that tend to remain without disintegration in the complete processes of ripening, harvesting, and drying result in the best dried samples. Plants must be long-lived to keep down yard maintenance costs and maintain high yields.

EARLY DEVELOPMENT OF VARIETIES

THE natural variability of the hop plant and the futility of attempting to propagate commercially by means of seed was recognized at an early date (13). In 1669, different types were distinguished, and by 1726 the existence of male and female plants was noted by European growers. Many varieties were known by 1799. The desirability of growing uniform sorts was also acknowledged though in England during the nineteenth century there was a great confusion of varieties.

During the development of the industry in the United States, as in Europe, many named varieties have been grown that, with the exception of the four now grown on the Pacific coast, have disappeared from commercial fields. Introductions of foreign types made from time to time by producers of extensive acreages have also vanished for the most part.

In the important years of production in New York several varieties grown included English Cluster, Grape, Canada Red, Palmer Seedling, and Humphrey Seedling. The latter types were also cultivated in California and in addition the so-called “American hop” was grown.  The Fuggles variety did not prove popular in California.

The earliest recognition by the Department of Agriculture of the need of improved varieties of hops in the United States was in 1900, when David Fairchild imported roots of the best European varieties.  After thorough tests it was found that these did not yield well enough to make their production under American conditions profitable.  In 1904 he started breeding work and crossed European varieties with American male plants. Prior to this American hop growers had from time to time sought to accomplish the same purpose in the same way with similar results.

In 1908 Stockberger (17) outlined a program he had undertaken in the Department of Agriculture. He referred to the failure of the earlier attempts to adapt European varieties and suggested a different procedure based on a recognition of the fact that the hop plant is greatly influenced by soil and climatic conditions, so that improvement by selection of the best varieties already being grown in this country would be simpler and give quicker results. He proposed a careful study of the domestic varieties, the selection of promising individual seedlings, and thereafter the development of desirable types by hybridization. Although the chief objectives he sought related to productiveness and quality, he stated that individual hop plants had shown a marked resistance to disease and that these were being propagated to determine not only whether that character is transmittable but to note their general qualities from other standpoints.

Progress on this project was reported in brief statements in the Yearbooks of the Department of Agriculture for 1911 and 1912 in which the selection of several promising hybrid seedlings and the continued introduction of foreign sorts is referred to. By 1916 several thousand seedlings were under cultivation. About this time a number of circumstances forced the abandonment of the project. A reduction in funds made a continuation of the field work impossible. The European war interfered with further importations of foreign varieties, and a few years thereafter the advent of prohibition greatly reduced the commercial importance of hops.

The investigations of State experiment stations have not until recently been directed toward problems concerning hop varietal improvement, and early Federal experiments have not been continuous.

Principally because of the inroads of downy mildew, experimental work with hops was initiated in 1930 by the Division of Drug and Related Plants of the Bureau of Plant Industry, United States Department of Agriculture, in cooperation with the Oregon Agricultural Experiment Station. The principal purpose of the program was to investigate disease control through field practices and to work toward the development of improved, disease-resistant varieties. Experiments have been in progress since that time. More recently varietal improvement of hops has been started by the New York (State) Agricultural Experiment Station at Geneva, as previously mentioned.

In Europe there seems to have been from early times a careful selection of stocks, varieties appearing and disappearing frequently.  Though the origins of many strains are obscure, numerous ones are known to have resulted from selection of chance seedlings and others by propagation from desirable plants. The Late Clusters variety is thought to have arisen from a chance seedling of the wild hop. The origin of Fuggles is typical of the development of many strains.  Concerning it Percival (6, p. 87) wrote:

   The original plant was a casual seedling which appeared in the flower-garden of Mr. George Stace, of Horsmonden, Kent. The seed from which the plant arose was shaken out along with crumbs from the hop-picking dinner basket used by Mrs. Stace, the seedling being noticed about the year 1861. The sets were afterwards introduced to the public by Mr. Richard Fuggle of Brenchley, about the year 1875.

Another old English variety, Colgate, was started from a likely looking plant found growing in a hedge. Bates Brewer was developed from root cuttings obtained from an outstanding plant that was paid for in whisky (6). Many of the continental varieties undoubtedly began with similar plant selections. The varietal history of hops closely resembles that of potatoes. Selections of seedlings by growers, followed by vegetative propagation, have frequently originated new types in both plants.

Fruwirth (4, pp. 77-88) assigned the origin of several early varieties, including Golding, Early Brambling, and Semsch, to bud variations, the variants then being propagated independently by cuttings. This is comparable to the bud or graft propagation of new apple types appearing on trees of old varieties.

Individual workers, not growers primarily, undertook independent investigations late in the last century. Fruwirth began selection of promising individuals in 1888. Other workers mentioned by Fruwirth were Stambach, who first planted seedlings in 1894, and Remy, who in 1898 was making studies of the resins and tannins of seedlings.  Early work also included that of Beckenhaupt at Weissenburg and Wagner at Weihstephan, Germany, who grew local and introduced varieties in comparative trials.

Organized efforts for hop improvement began fairly late in the last century. A testing garden was established near Saaz, Bohemia, in 1897, and many varieties were grown. Breeding by seedling selection had begun in Belgium by 1903.  About 1898 the Agricultural College of Wales began investigations on hop improvement, and breeding was undertaken in 1907.  One of the oldest and most active investigational projects has been in progress in England since about 1904. In 1913 visitors to the college hop nursery at Wye, Kent, selected promising seedlings for trial and subsequently 2,830 cuttings from 23 varieties were supplied to growers. A testing station especially for determining brewing value was established at East Malling in 1917 and has made important contributions to the English work. By 1911 Denmark had begun variety investigations. Additional stimulation was given to hop breeding in Europe generally by the severe losses due to downy mildew in 1926 and 1927. In 1926 a society for hop research was founded in the Hallertau district of Bavaria. In 1932 a large German hop company placed its acreage at the disposal of the government for testing purposes. The work of hop selection in the Union of Soviet Socialist Republics, undertaken by the Agricultural Academy of Moscow, began in 1926. In addition to those mentioned, other state, governmental, and private agencies in Europe are concerned with varietal improvement of hops. In the appendix are listed some of the workers and the countries in which experimental work is in progress.

RECENT BREEDING WORK

The improvement of hop varieties concerns the cone-bearing female individuals particularly. When seeded hops are grown, male plants that produce abundant pollen at the time of the flowering of the female plants are needed. Thus selection of desirable male plants may be necessary.

Considering grower and trade demands, an ideal variety would embody resistance to downy mildew, high yield, suitable resin content, and good aroma. It would be medium leafy, easily picked, resistant to insects, and capable of remaining on the vines a reasonable time after maturity without deterioration. Excessive fragility and large stems would be undesirable. This indicates the varied character of the hop-breeding problem. Meanwhile, new diseases or other troubles may appear to provide additional complications. Considering all these points, no varieties commonly grown at present quite "fill the bill.”

Recent work has developed along several important lines. In 1930 and 1931 an extensive survey was made of the plant material being grown in commercial yards of Oregon, to determine the possibility of selection of superior types in old hop yards. In 1935 a similar, though less comprehensive, inventory was made in coastal California. Superficial examinations have also been made of a few Yakima Valley yards in Washington. The general result of these surveys has been failure to find occasional plants, which might be propagated as improved types, strikingly superior to the general lots of the four important varieties.  There has frequently, however, been a varying percentage of inferior sorts, the elimination of which would allow a sizeable increase in production. Such types have been chiefly hermaphrodites6 and sterile plants producing no flowers, often called bastard hops by growers. In many yards male plants are unnecessarily numerous for pollination purposes. Additional work is being done on vegetative selection among commercial varieties and the breeder is constantly watching for superior individuals.

In all plant improvement one of the most promising methods of obtaining better types is the introduction of varieties from foreign countries having growing conditions comparable to those in our own hop areas. Experience has not been promising as to the value of this practice in hop improvement, but it is hoped that useful breeding material will be acquired by this means. Beginning in 1931, attempts have been made to obtain propagation stock of superior English and continental varieties to grow in the experimental nursery at Corvallis, Oreg., in comparison with domestic sorts. Though some European countries have prohibitions against the exportation of cuttings, in all about 35 foreign strains have been obtained by the Division of Plant Exploration and Introduction and are now being grown. Cuttings for propagation improperly packed are perishable and in some instances difficulty has been experienced in obtaining living roots shipped long distances. Plants from imported cuttings do not usually bear hops until the second year.

The third method of attack that may be used for variety improvement is the selection of superior plants from those grown from seed.  This plan appears to offer most promise. Since it is difficult to designate male individuals according to variety, all seeds produced may be considered of hybrid nature. Thus seed may be collected from any good female in the hope that some of the progeny will excel the mother plant in various characters. The nature of the male parent in such a case is unknown. It is also possible to obtain seeds from plants that have been pollinated artificially. In these cases the nature of the male is known, and vigorous, desirable types may be used. When controlled pollination is practiced, the female flowers are covered with small bags and pollen of the male plant is shaken over the blossoms. A plant undergoing artificial pollination is illustrated in figure 2.


Figure 2—Vines of the Late Clusters variety of hops, with side branches covered with glassine bags to control pollination. Bags are held in place by paper clips, and operations are recorded on small marking tags attached to the stems.


HOP YARDS FOR EXPERIMENTAL TESTING

The experimental field at Corvallis, Oreg., consists of an area trellised and spaced like a commercial yard and another smaller section for growing seedlings for the first year’s observations. The larger area, pictured in figure 3, is capable of accommodating about 3,500 plants spaced 8 feet apart. Included in this section are plantings of all domestic and available foreign varieties, together with seedling plants that appear worthy of growing beyond the first year. The smaller area, known as the seedling yard, is designed for growing first-year seedling plants for preliminary observation. Seedlings are planted 15 to 18 inches apart in the row and trained on strings attached to a wire approximately 6 feet from the ground level. About 3,000 plants may be grown under these conditions (fig. 4). Seedlings that appear to be of the types sought are then transplanted to the standard yard for further tests. Hop seeds may be sown in greenhouses or in coldframes in the field in early winter or early spring. In the growing season the plants obtained are moved into the seedling yard or into field rows to be later included in the nursery. Seedlings growing in greenhouse beds are shown in figure 5.


Figure 3.—View of experimental yard showing plant variation among hop seedlings. Those in the foreground are superior types.



Figure 4.—First-year hop seedlings in nursery yard. Note closeness of planting and variable growth.


Figure 5.—Seedling hops in greenhouse beds. The dome lamps may be used to supplement daylight during fall and winter months. Strong seedlings are thus developed for field planting in the early spring.

Though, in general, growing conditions are kept favorable for plant growth in the experimental areas by following common commercial methods, the nature of the information sought requires certain widely divergent practices. One of these is the actual fostering of the development of the downy mildew disease by cultural practices favorable to its spread so that it will "run wild” among both the older plants and the seedlings under observation. Since resistance to this malady is one of the chief goals, its rapid spread is sought, to permit selection of resistant types.  Where it may seem apparent that plants vary in reactions to insects, the latter pests may also be left uncontrolled. Since it is not desirable to select plants under soil conditions exceptionally favorable for growth, the use of fertilizers is restricted. Otherwise, plants are allowed to develop in a manner comparable to those in commercial yards.

During the growing season many types of observations are made.  The development of downy mildew and the plant’s reaction to it are recorded weekly for some 3,000 seedlings and foreign and domestic varieties. Data are also taken on infestations of aphids and red spider. Relative maturity, vigor, stem and leaf color, leafiness, abnormalities, and sex are also recorded in seasonal notes previous to harvest.

Late Clusters, Early Clusters, and Fuggles are grown in plots of sufficient size and number of plants to obtain information on yields.  In 1934 and 1935 over 400 such plants were picked and weighed individually. Other less common varieties, such as Red Vine and Bavarian, are also grown though less extensively. Foreign strains and all promising seedlings are harvested individually but have not been grown on a comparative yield basis, for reasons indicated later.  After picking, samples are dried in a small experimental drier (fig. 6) through cooperation with the Oregon station section of agricultural engineering. The hops are then pressed into small bales resembling the commercial package except in size.


Figure 6.—Experimental hop-drying chamber.  The small cabinet within contains the samples of hops, placed in coarse mesh bags. The scale beam allows constant checking of moisture losses as the charge is dried. Drying temperature and heated-air flow may also be recorded.

Chemical tests have been made on many samples to determine the soft-resin content as a means of obtaining some index of quality.  Physical examinations have also been made for color, aroma, seed content, cone size and condition, and presence and appearance of lupulin. At present, the chemical and physical analysis of the dry hops is the ultimate test for brewing value. Actual brewing tests will be necessary to finally establish the suitability of new strains for commercial use.

BREEDING OBJECTIVES AND PROGRESS

In the hop-breeding project thus far, definite information has been obtained on a number of problems, and observations made since 1930, together with contacts with growers and dealers, have served to crystallize objectives.

Late Clusters, the dominant domestic sort, is normally a good yielder, has a high soft-resin content, and is otherwise well suited to brewing purposes. It is, however, quite susceptible to downy mildew, plant lice, and red spider. It is also leafy and late in maturity.  Early Clusters is very susceptible to downy mildew and aside from being somewhat earlier is interchangeable commercially with Late Clusters. The cones are larger and the vines a little less leafy. It is a favorite with pickers. Fuggles is resistant though not immune to downy mildew, usually making a fair crop when cluster varieties are severely injured. Yields are decidedly lower than those of the Early Clusters and Late Clusters and the variety does not permit as much delay in harvest as does Late Clusters. It is also quite susceptible to red spider injury. The soft-resin content of Fuggles is usually below that of the cluster types and the commercial trade recognizes the variety as an individual class.

Red Vine hops have been grown more extensively in earlier years than at present; very few uniform fields of this variety now exist.  It is noted for its pleasing aroma and many growers believe a small amount of Red Vine hops adds in this respect to the quality of Late Clusters. The soft-resin content is comparable with that of Late Clusters. Chief objections to Red Vine are leafiness, many small hops—though the yield is good—late maturity, and susceptibility to aphis, which is due in part to profuse foliage.

Where suitable males are present, all of these varieties produce abundant seed, but the prevention of seeding might easily be accomplished by elimination of male plants. Inability to obtain satisfactory premiums for seedless hops has not encouraged growers on the Pacific coast to eliminate seeds.

None of 30 varietal strains introduced from other hop-growing countries has appeared to be superior or equal to those now grown on the Pacific coast. This may be comparable with the results of extensive corn trials in the United States where many varieties do well only within small areas or localities. Certain of the introduced varieties have made fair growth and several have exceeded Late Clusters in percentage of soft resins. In table 1 are given results of physical and chemical analyses of some foreign and domestic hops grown at Corvallis, Oreg., in 1935. Though the data are for 1 year only, the analyses are remarkably high.

TABLE 1.—Physical and chemical analyses of hop varieties and seedlings grown at Corvallis, Oreg., 1935
Variety or seedlingColorAromaLupulinConesTotal soft resin (%)*
Foreign varieties:
Landhopfen
Yellow greenStrong, pleasantYellow, very plentifulMedium20.88
BurgunderGreenish golden yellowPleasant, flowerySmall19.92
Bavarian**Yellowish greenMild, pleasantLemon yellow, plentiful19.17
AlsacePale greenStrong, not pleasantMedium18.60
GoldingGreenish golden yellowMild, not pleasantYellow, plentifulSmall to medium17.87
M 45Yellowish greenMild, pleasantMedium17.70
SpalterPale greenExcellent, flowery17.54
ElassarYellowish greenVery pleasant, flowery17.54
Domestic varieties:
Late Clusters
Mild, agreeableLemon, yellow, very plentifulSmall to medium19.12
Early ClustersGolden greenStrong, pleasantYellow plentifulMedium to large18.58
FugglesMild, very pleasantLemon yellow, plentifulMedium17.62
Red VineGolden yellowStrong, not pleasantYellow, plentifulLarge17.11
Seedlings:
52-31
Pale greenStrong, pleasantLemon yellow, plentifulMedium to large19.71
8-12Yellowish greenMild, agreeableLemon yellow, very plentiful19.06
62.27Pale greenMild, pleasantYellow, plentifulSmall to medium18.12
101-32Bright greenVery mild, pleasantVery plentifulMedium to large17.75
36-32Pale greenMild, pleasantPlentifulSmall to medium17.70
73-12Yellowish greenStrong, unpleasantVery plentiful17.20
70-13Pale greenMild, pleasantYellow, plentifulMedium17.16
*Based on air-dry hops.
**Of uncertain origin, possibly a domestic selection by growers.


The soft-resin content is based on individual determination of several resin components, which is the usual method of chemical analysis. The notes on physical characteristics of the various lots are of importance, since commercial dealers usually observe these points in trade samples. Comparisons may be made between foreign and domestic varieties by reference to the table. Though all of the samples listed might be considered choice from a trade viewpoint, superiority of certain strains is indicated. In both 1934 and 1935 Landhopfen and Burgunder exceeded Late Clusters, the richest domestic variety, in percentage of soft resins.  Analyses of certain of the better seedling selections indicate the possibilities for obtaining improved types in this important character.

Wide variations in physical traits may be noted, though soft-resin contents remain similar. Aroma particularly may vary from excellent to strong and unpleasant when other characters seem to vary but little.

Many seedlings have been grown at Corvallis since 1931. Seed has been obtained from domestic and foreign varieties from the experimental yard and from many commercial fields. These seedlings have been for the most part of inferior types. Many are male plants, others are dwarfed or otherwise undesirable, and only rarely is a plant producing "fair” hops obtained. One of the latter sorts, considerably better than usual, is illustrated in figure 7.


Figure 7.—A promising seedling hop plant having a cone type resembling Fuggles and leaves similar to those of Late Clusters.

In the matter of soft-resin content, seedlings may vary over a wider range than varieties. In the 1933 season 29 of these varied from 9 to 17.9 percent,7 while Late Clusters contained 17.9, and Fuggles 16.3 percent soft resins. In the crop of 1934 cones from 57 seedlings contained between 9.4 and 17.8 percent of soft resins. The percentage for Late Clusters was 17.8 and for Fuggles 14.8. Nineteen foreign varieties grown at Corvallis under similar conditions ranged from 14.2 to 19.4 percent soft resins. Similarly, the 1935 crop of 50 seedlings ranged from 11.1 to 19.7 percent; Late Clusters contained 19.1 and Fuggles 17.6 percent. Foreign varieties, 23 in number, varied from 14.1 to 20.9 in percentage of soft resins.

In aroma, many seedlings have compared to advantage with standard varieties while some are decidedly inferior.

Experience has demonstrated, both here and abroad, that plant reaction to downy mildew is difficult to ascertain. This is due to the irregularity of the occurrence and development of the disease. The nature of this problem may be indicated by the fact that one seedling of a very promising nature in the years 193 1-33, free from mildew and of good agronomic appearance, mildewed severely in 1934 and 1935.  Preliminary tests have shown that artificial inoculation of questionable plants by hypodermic injection of the mildew organism may be feasible. This would tend to supplement the work of nature in the development of the disease and make possible more rapid progress.  Results at Corvallis offer some assurance of obtaining seedlings resistant to the downy mildew disease.

Since yields of foreign types have been obviously inferior to those of commercial varieties, comparative yield tests of the former with domestic sorts have not been made.  Neither have any of the foreign varieties proved to be highly resistant to downy mildew.

Results thus far indicate that leaf, stem, cone form, and cone arrangement are fairly constant from year to year. Plants producing male or female or both types of flowers in any one year tend to be similar in other years though occasionally marked exceptions may occur.

Resistance to aphids and red spider has not been found in any varieties or seedlings observed. Though many plants have not been injured, several years’ observation, as in the case of reaction to downy mildew, will be required to definitely determine the stability of this character.

In summary, of the improvements sought, agronomic characters, including high yield and desirable cone type, have proved to be the most difficult of attainment, judging from recent experience in the breeding project. Between 15,000 and 20,000 seedlings, of which approximately 3,000 have been grown to the cone-producing stage, have allowed selection of fewer than 10 with records of resistance to mildew, high resin content, and good agronomic qualities. Most of these may not survive continued tests.

It is proverbial among plant workers that varietal improvement usually requires consistent work over many years before great practical benefits can be shown. While propagation by cuttings simplifies the plant breeder’s job in that plants “impure" from the hereditary standpoint may be reproduced as uniform, true-breeding commercial varieties, in the case of hops this advantage is counterbalanced by problems not usually met in such work.

Large Numbers of Plants Needed for Effective Selection

Caring for large numbers of plants individually during a period of several years requires a large area and much labor. Picking and drying many samples separately and the making of chemical tests also present physical problems. All of these limitations mean that the work is necessarily slow.

Growers of the Pacific coast have shown new concern in improvement problems since 1931. Of interest in this regard also is the initiation of the varietal improvement project by the New York (State) Agricultural Experiment Station, previously mentioned.

Though European varieties have not to date proved to be adapted to conditions on the Pacific coast, the progress made in developing improved types in Europe by seedling selection offers hope for comparable progress in the United States.

Mildew Records

An obstacle common to all breeding for resistance to disease is the frequent necessity of waiting for natural development of epidemics before plant reaction can be obtained. Downy mildew appears capriciously, and 8 to 10 seasons may be required to adequately determine plant reaction to this disease. Yield and quality are variable characters requiring tests of several seasons’ crops.

Methods of recording and comparing data on downy mildew reaction from season to season have presented a troublesome problem. At present such notes are taken at approximate weekly intervals while the epidemic is spreading, and plants are classified by numbers from 0 to 5 as representing progressively increasing numbers of leaves or branches infected by the disease. Comparative classifications of 2,827 plants upon which notes were taken in 1934 and 1935 are given in table 2. The differences of reaction from year to year due to variation in the development of the epidemic through the area are indicated. In 1934, for example, 294 plants were classified as no. 5 in reaction, or very susceptible. Of these, 183 failed to develop symptoms in 1935. Of the 1,788 plants classed as 0 in 1934, 1,543 did not mildew in 1935. The data show that even with downy mildew generally present, many susceptible plants may escape infection.

TABLE 2.—Downy mildew, incidence in experimental yard, Corvallis, Oreg., 1934-35
1935 classification*Plants in each classification* in 1934Total
012345
01,5439930458621832,249
14127361069
2165892222060367
320242212
41021015
53632515838125
Total1,788112432103982942,827
*0 to 5 represents progressively increasing numbers of infected leaves or branches.


Seasonal Productivity

Various agronomic reasons for unproductive hills were suggested by Bressman (1), and Stockberger (19) indicated certain conditions influencing yields. Attempts have been made to determine the consistency of yield of hop plants (18) from year to year. Growers often experience unexplainable irregularity of development and production in yards usually uniform. The question has arisen also as to the possibility of continuously selecting from the most vigorous plants as a means of increasing yield by isolation of more vigorous types. Information is being sought that will answer these questions more completely.

In 1934 and 1935 hill surveys were made of 25 different marked areas of 100 hills each in some 15 yards, on several soil types in western Oregon. Plants were classed as S (strong), M (medium), W (weak), X (untrained—also a weak type) and O (indicating no plant present), at two periods in each season. A contingency table (table 3) shows the relations between 1934 and 1935 notes taken just previous to harvest. Hills designated as O in 1934 were replanted in the early spring of 1935. The data indicate unexpected irregularity in the seasonal growth and productivity of any particular class of plants. Frequently individuals classified as strong in one season may be considered as weal or even fail to produce hops the succeeding year. Continuation of records may provide information serving to throw light on such variations.

TABLE 3.—Summary comparing hill survey of plant types, commercial yards, Willamette Valley, Oreg., 1934-35
1935 classification*Plants in each classification in 1934Total
SMWXO
S390512162195773
M165498960336
W8519133227437
X100962954
O45027551128
Total69556441744621728
*S=strong; M =medium; W =weak; X=untrained; O=no plant present.

Production data add more precisely to the interpretation of this problem. Actual yields on individual plants from the experimental yard in 1934 and 1935 are available on the Late Clusters, Early Clusters, and Fuggles varieties. Correlations between yields of the two seasons dare indicated in table 4.

TABLE 4.—Yield data for three varieties of hops, 1934-35
VarietyPlants
(Number)
Mean yieldr valueP value
exceeds—
19341935
Late Clusters1047.9±0.5012.14±0.490.190.05
Early Clusters1137.19±.407.94±31.57.01
Fuggles1255.60±.207.26±.19.39.01

In general a significant relation between yields from year to year is exhibited, although the correlation coefficient for Late Clusters is marginal.

Other Important Technical Studies

Analyses of the results of artificial pollination have been complicated by two major problems—(1) the slow and irregular germination of hop seeds, and (2) the doubtful results of bagging.  Somewhat detailed studies have shown greatly increased and more rapid germination as a result of cold treatments. One of the best of the treatments used was placing the seeds in moist blotters in a germinator for 5 days at room temperature followed by refrigeration for 5 weeks at 5° C.  Such procedure has increased germination from less than 10 to over 70 percent.  Once seeds have germinated and plants have emerged, growth may be rapid. Artificial illumination has been reported by Bressman (2) as of value in stimulating vegetative development.

Results of bagging and subsequent pollinations have been inconclusive. Some seeds have developed within and outside of glassine and parchment bags whether or not enclosed flowers were artificially pollinated. The bags used have been tightly secured to the branches by paper clips. Flowers have been covered at various early stages of development, from the period immediately preceding the appearance of the stigmas through the time when they withered. Whether plants form seed parthenogenically, without fertilization, or whether seed obtained from bagged, unpollinated flowers will grow has not been satisfactorily determined. Thus far the possibility of incomplete exclusion of pollen from bagged flowers does not seem adequate to explain the results obtained. Winge (20), Howard (5), and others, however, have reported the failure of seeds to set when pollen was not allowed to reach bagged flowers. Relations between ability of male pollen from different plants to cause fertilization and ability of females to produce seed are also being determined. Until seed formation and germination can be more accurately controlled, the results and the value of hybridization will be uncertain.

Constancy in development among various plant characters from year to year is indicated in table 5. Fundamental information is needed in this respect to form a basis for plant selection.

TABLE 5.—Constancy of plant vegetative characters
1935 classificationPlants in each classification in 1934
DwarfsDwarfedWitches' broomRaggedRussetedColored vinesTotal
Dwarfs2000013
Dwarfed136112124
Witches' broom001700017
Ragged19173651866188
Russeted4305291455
Colored vines614044265293
Total4440217553347580

Descriptive differentiation of the classifications seems unnecessary to illustrate the variations in vigor and type of growth from season to season. With the exception of colored vines, other classes are plant weaknesses and therefore undesirable. Occasionally vigorous plants of good general type may show light russeting of leaves. Ragged plants develop torn or ragged leaves and flowering branches may be partially or entirely sterile. The type known as “witches’-broom" is apparently the sterile dwarf described by Salmon (7).  It is possible that some of the conditions listed may be pathological while others may be due in part to genetic factors. While detailed notes are available for 2 years only, a marked constancy of growth character is evident in certain groups.

In dioecious species such as hops the expression of sex is of particular interest. Development of hop plants as to sex appears to be generally constant though infrequent, wide deviations apparently occur. It is a fairly common observation of growers that in some years more male plants appear than usual.

In approximately 1,200 seedling plants in the experimental yard upon which notes have been taken for sex, the following deviations occurred in 2 years, 1934 and 1935:

Plants
Change from male to female5
Change from male to hermaphrodite82
Change from female to male1
Change from female to hermaphrodite1
Change from hermaphrodite to male2
Change from hermaphrodite to female5

Deviations may be noted in all degrees of sexual expression. Data are insufficient to justify generalizations as to which transformations occur most frequently or to suggest possible explanations. Observations of Chartschenko (3) in this respect are noted later, Salmon (7) has recorded relative frequencies of male and female individuals in seedling progenies, as well as other developmental types.

The variation to be expected in resin analysis of hops from the same plants from year to year is a factor requiring careful study.  Even though individuals are harvested at as nearly the optimum time as possible and all other factors are controlled similarly, large differences may exist from season to season. This is illustrated in table 6, comparing examples taken at random from yearly analyses of individual plants.

TABLE 6.—Soft-resin contents of hops from individual seedling plants
Seedling no.Soft-resin content for—*
(%)
193319341935
36-718.2217.9516.03
53-1017.1016.9615.93
19-3317.4916.7714.36
62-2717.5314.9318.12
8-1018.7017.6116.77
56-2814.6010.2412.88
*Percentages on dry basis.

The data show the relative inaccuracy of analysis of a single year’s crop as a strict indication of plant behavior, at least for some individuals. Plants might, however, be placed in general groups as good, fair, and poor, with reasonable accuracy in most instances. Increased experience and additional care in harvesting, drying, and packaging of samples will undoubtedly decrease the errors encountered.

CONTRIBUTIONS BY VARIOUS INVESTIGATORS

A brief review of investigated points of interest in hop breeding will indicate the nature of some of the problems and the facts obtained in other hop-growing countries. Though hops were investigated at an early date, comparatively little information on breeding aspects may be found in the literature. Reference has already been made to certain work. An attempt to bring together scattered supplementary facts and further outline the general background seems desirable.

It was early noted that plants from seeds were variable and most often poor (13). A wide range of maturity was also noted in such progenies (15). In addition it was recognized that new varieties might arise either from seeds or from bud variations.

Salmon (7). obtained the following results from seed progenies derived from controlled pollinations:
   From 256 seeds 87 seedlings were produced, of which 52 plants were normal and 35 were sterile dwarfs.
   From 285 seeds 67 seedlings included 66 fertile and 1 dwarf plant.
   From 261 seeds 120 plants, all of normal vegetative growth, included 108 females, 111 males, and 1 hermaphrodite.
   From 899 seeds 109 seedlings included 79 normal plants and 30 sterile dwarfs.

The dwarf plants made little growth compared to normal plants and failed to form flowers of any kind. Such results represent the expected appearance of many inferior plants in seed progenies, however derived. Studies of three groups of seedlings reported by Fruwirth (4) indicated the proportions of female plants to be 66, 77.7, and 90 percent respectively, in the progenies considered.

Pollinated cones were found by Winge (20) to be larger and heavier than those whose flowers were not pollinated. Unpollinated hops were observed to remain longer in the bur, and stigmas at the stem end were noted to appear first (5). Fertilized cones were also thought to mature earlier and resist mold to a greater degree than those unfertilized.

In order that pollination might be complete, it was recognized that male plants must shed pollen throughout the bur period of the females.  Pollen from hermaphroditic plants was determined to be viable and to be capable of fertilization (20). Chartschenko (3) reported female flowers of such plants to produce viable seed.

The impossibility of crossing two female plants has been pointed out, though combinations of female varietal characters in one individual may often be desirable. In addition it seems obvious that since male plants do not bear hops, their value in use as parents must be determined with appreciable difficulty.

As early as 1894 Stambach, cited by Fruwirth (4), planted out seedling hops for observation. Remy, mentioned by the same writer, studied resins and tannins of seedling hops in 1898. He crossed cultivated female varieties with wild males, crossed an F1, or first generation, male of the progeny with a cultivated female plant, and then recrossed an F1 male of the latter progeny back to a cultivated female. This is a comparatively complicated crossing scheme but is occasionally used by plant breeders.

Reversals in the nature of the sexual character of hop plants have been reported by several workers, according to Fruwirth (4). Chartschenko (3) has given examples of sexual changes. A male plant was described as changing to a normal female in 2 years, being a hermaphrodite in the third, and a normal male again in the fourth year. In another case a cutting from a female plant produced a vine bearing male flowers. In yet another instance two female plants changed to hermaphrodites. Vegetative increase of these also gave rise to hermaphrodites.

Much interest has been shown in studying relations of numerous plant characters to the important property of resin content and other indications of quality. Fruwirth (4) reported high yield to be associated with inferior aroma, greater foliage production, stouter strigs (center stem of cone), and plant longevity. Chodounski, mentioned by Fruwirth, thought coarser hops to be characterized by inferior hairing, lack of uniformity in strength, abnormal structure, and other characters of the strig. Sutora, cited by the same writer, concluded that a coarser strig and darker green color of the hop is associated with a lower tannin content. According to Fruwirth, finer hops were thought by Wagner to have smaller bracts and a smaller bract area. Percival (6) pointed out that delicacy and weakness of cones were often met with in hops of the best quality. Salmon has indicated that a theoretically choice English hop might combine high soft-resin content with the aroma of present English or Saaz varieties (8). He stated that total resin contents remain fairly constant from season to season in varieties generally (9). Chartschenko (3) reported that Russian work had failed to establish any female characters as being associated with resin content. Within varieties no significant relation was found between resin content and yield of green hops or earliness of ripening, or in most cases between earliness and yield of green hops.  Appreciable variation was found as to resin contents between vegetative selections within varieties. Results of analyses of male plants in which resin contents varied from 1.77 to 3.48 percent were given. Attention was directed to the importance of this in view of the fact that the male contributes half the inheritance of the progeny in this and other characters.

It has been accepted that variety has more to do with resin and oil content of hops than soil or locality. Other factors that influence these characters are climate, fertilizers, maturity, drying methods, and seed content. The aroma of certain types of American hops has been compared with the odor of turpentine, black currant leaves, onions, rue, and apples, and therefore said to be inferior to that of European hops (8).  Resin content (14) and aroma (16) have been found to be inherited traits and progeny plants may exceed the female parent in these important attributes.

In one instance of a cross, the aroma of an Oregon female plant was exhibited by about three-fourths of its progeny. Aroma has been shown to be transmitted through the male, by the same investigator (16).

Characters recognized as constituting differences among varieties have included vine color and length of internodes; maturity, arrangement, and form of strobiles; color, number, and form of leaves; leafiness in proportion to cones and stems; and relative dry weights of the cones. Though variation seemed less marked in males, they were found to be generally as variable as female plants (22).

American varieties introduced into England have proved to be unsuited there and it has been concluded (8) that introduction of foreign varieties has little value except for use as parents in obtaining superior seedlings. This may represent the major value of varietal introductions made into the United States.

Since the appearance of downy mildew in European hop culture, attention has been directed to varietal response to this and other diseases. Salmon (9) has reported many of these results, which eventually have served to classify all varieties as mildew-susceptible though in varying degrees. Saaz hops, at first thought to be immune, mildewed in 1932. Fuggles is one of the most resistant types, but both leaf and cone infection have occurred. Some strains may be resistant to cone infection. Many of the most resistant sorts are now in commercial use. Salmon (10) has also observed certain varieties and seedlings to be resistant to blue mold.

In England the “mosaic disease”, so called because of its mottled coloring effects on the leaves, affects all hops except the varieties Fuggles, Tolhurst, and Colgate. Nettlehead and chlorotic diseases have been found only on Fuggles (8). In 1926 mosaic disease was serious in Yugoslavia. Mosaic disease, nettlehead, and the chlorotic diseases are virus9 troubles not generally reported from hop-growing countries.

Crossing experiments with hops have been carried out in most European countries since 1900. Hybrids between Humulus neomexicanus and H. lupulus have been reported (11). Imperfectly formed seeds of H. lupulus and H. japonicus have been obtained (20), but these have failed to produce plants.

Cytologic investigation has received little attention to the present time, though Winge (20, 21) has studied the genus Humulus in some detail. Chromosome numbers in H. lupulus have been found to be 20 in the vegetative cells (diploid). These have been designated as 18+2X in the female and 18+X+Y in the male. In H. japonicus 17 have been assigned to the male (14+3X) and 16 to the female (14+2X) (21).

Absence of more complete information on inheritance of plant characters is undoubtedly due to the sexual nature of the hop species and attendant problems in obtaining satisfactory progeny tests.  As previously mentioned, the situation approaches that in higher animals.

BREEDING PROGRAM SLOW BUT PROMISING

Isolation of improved varieties of hops resistant to downy mildew and otherwise superior to present domestic sorts appears to be reasonably practical. Present objectives in hop breeding are well recognized and methods of reaching desirable ends are in the process of establishment. Results obtained in England indicate promise for consistent investigation. Hop breeding experiments initiated at Wye, Kent, in 1907 have resulted in significant improvements of the English crop.  Salmon (12) has recently announced the development of two valuable new varieties, Brewer’s Favourite and Brewer’s Gold. The first of these is a seedling originating in 1909 from a plant of Oregon Cluster (probably Late Clusters) introduced into England, and it has been tested extensively since that time. Brewer’s Gold is also a seedling, first raised in 1919. These varieties are high yielders, producing cones rich in soft resins and otherwise acceptable to both brewer and grower.

Based upon breeding investigations with crops of other kinds as well as hops, continued experimentation will be necessary if progress is made such as has been reported in other countries. The breeding project requires observation of numerous plants in comparative field and chemical tests over a long period.

LITERATURE CITED

 (1)  Bressman, E. N. 1931. UNPRODUCTIVE HOP PLANTS AND VARIETIES IN OREGON. Jour. Inst. Brewing 37 (n. s. 28): 372-377, illus.
 (2)  ―1931. DEVELOPING NEW VARIETIES OF HOPS. Science (n. s.) 74: 202-203.
 (3)  CHARTSCHENKO, N. 1934. zUR FRAGE DER METHODIK DER HOPFENZÜCHTUNG. Zuchter 6:113-119, illus.
 (4)  Fruwirth, C. 1924. HANDBUCH DER LANDWIRTSCHAFTLICHEN PFLANZENZUCHTUNG. Aufl. 4 .. .,v. 3 illus. Berlin.
 (5)  Howard, A. 1905. THE INFLUENCE OF POLLINATION ON THE DEVELOPMENT OF THE HOP. Jour. Agr. Sci. [England] 1: [49]-58, illus.
 (6)  PERCIVAL, S. 1901. THE HOP AND ITS ENGLISH VARIETIES. Jour. Roy. Agr. Soc. England 62: 67-95, illus.
 (7)  Salmon, E. S. 1914. ON THE APPEARANCE OF STERILE “DWARFS" IN HUMULUS LUPULUS L. Jour. Genetics 3: 195-200, illus.
 (8)  ―1917. THE VALUE OF HOP-BREEDING EXPERIMENTs. Jour. Inst. Brewing 23 (n. s. 14): 60-97.
 (9)  ―1918-35. [REPORTS OF THE TRIALS OF NEW VARIETIES OF HOPS.] See Southeast Agr. Col., Wye; East Malling Research Sta., Kent; and Jour. Inst. Brewing for various years.
(10)  ―1921. ON FORMS OF THE HOP (HUMULUS LUPULUS L.) RESISTANT TO MILDEW (SPHAEROTHECA HUMULI (DC.) BURR.); V. Ann. Appl. Biol. 8: 146-163.
(11)  ―1930. HOP-BREEDING EXPERIMENTS, 1917-30. Jour. Inst. Brewing, 36 m. s. 27): 578-591, illus.
(12)  ―1934. TWO NEW HOPS: “BREWER’S FAVOURITE” AND "BREWER’S GOLD." Jour. Southeast Agr. Col., Wye, Kent 34: 93-106, illus.
(13)  ―and Wormald, H. 1921. A STUDY OF THE VARIATION IN SEEDLINGS OF THE WILD HOP (HUMULUS LUPULUS L.). Jour. Genetics, 11: 241-267, illus.
(14)  SCHMIDT, J. 1915. JoHS. SCHMIDT: INVESTIGATIONS ON HOPS (HUMULUS LUPULUS, L.). VI. ON THE AMOUNT OF LUPULIN IN PLANTS RAISED BY crossiNG. Compt. Rend. Lab. Carlsberg 11: [165]-183.
(15)  ―1915. JOHS. SCHMIDT: INVESTIGATIONS ON HOPS (HUMULUS LUPULUS, L.). VIII. ON THE FLOWERING TIME OF PLANTS RAISED BY CROSSING. Compt. Rend. Lab. Carlsberg 11: [188]-198.
(16)  Schmidt, J. 1917. JOHS. SCHMIDT: INVESTIGATIONS ON HOPS (HUMULUS LUPULUS, L.). X. ON THE AROMA IN PLANTS RAISED BY CROSSING. COmpL Rend. Lab. Carlsberg 11: [330]-332.
(17)  STOCKBERGER, W. W. 1908. IMPROVEMENT OF HOPS BY SELECTION AND BREEDING. Amer. Breeders’ Assoc. Proc. 4: 156-161.
(18)  ―1912. A STUDY OF INDIVIDUAL PERFORMANCE IN HOPS. Amer. Breeders Assoc. Ann. Rept. 7-8: 452-457.
(19)  ——— and THOMPSON, J. 1910. SOME CONDITIONS INFLUENCING THE YIELD OF HOps. U. S. Dept. Agr., Bur. Plant Indus. Circ. 56, 12 pp., illus.
(20)  Winge, O. 1914. JoHS. SCHMIDT: INVESTIGATIONS ON HOPS (HUMULUS LUPULUS, L.). III. THE POLLINATION AND FERTILIZATION PROCESSES IN HUMULUS LUPULUS L. and H. JAPONICUS SIEB. ET zucc. Compt. Rend. Lab. Carlsberg 11: 1-44, illus.
(21)  ——1929. ON THE NATURE OF THE SEX CHROMOSOMES IN HUMULUs. Hereditas 12: [53]-63, illus.
(22)  Wormald, H. 1915. VARIATION IN THE MALE HOP, HUMULUS LUPULUS, L. Jour. Agr. Sci. [England] 7: [175]-196, illus.

GENERAL REFERENCES TO LITERATURE ON HOP PRODUCTION, CULTURE, AND IMPROVEMENT

Braungart, R.
1901. PER HOPFEN ALLER HOPFENBAUENDEN LANDER DER ERDE ALS BRAUMATERIAL. 898 pp., illus. München and Leipzig.
Flint, D. A.
1900. HOP CULTURE IN CALIFORNIA. U. S. Dept. Agr. Farmers’ Bull. 115, 28 pp., illus.
HOERNER, G. R.
1932. DOWNY MILDEW OF Hops. Oreg. State Agr. Col. Ext. Bull. 440, 11 pp., illus.
MEEKER, E.
1883. HOP CULTURE IN THE UNITED STATES; BEING A PRACTICAL TREATISE ON HOP GROWING IN WASHINGTON TERRITORY FROM THE CUTTING TO THE BALE. 169 pp., illus. Puyallup, Wash.
Myrick, H.
1899. THE HOP; ITS CULTURE AND CURE, MARKETING AND MANUFACTURE . . .299 pp., illus. New York, Springfield, Mass. [etc.].
ParkER, H. H.
1934. THE HOP INDUSTRY. 327 pp., illus. London.
Salmon, E.S., and Ware, W. M.
1931. THE HOP DOWNY MILDEW AND ITS CONTROL. Pub. Univ. London, Dept. Econ. Mycology, Southeast Agr. Col.,, Wye, Kent.
STOCKBERGER, W. W.
1922. GROWING AND CURING HOPS. U.S. Dept. Agr. Farmers’ Bull. 304, 36 pp., illus.
Sulerud. G. L.
1931. AN ECONOMIC STUDY OF THE HOP INDUSTRY IN OREGON. Oreg. Agr. Expt. Sta. Bull. 288, 77 pp.. illus.

APPENDIX

WORKERS AND STATIONS CONCERNED WITH VARIETAL IMPROVEMENT IN HOPS AND HOP BREEDING11

R. E. Alexander, Canterbury Agricultural College, Lincoln, New Zealand.
A. Arkhangelsky, Plant Breeding Experimental Station, Moscow Agricultural Academy, Moscow, Union of Soviet Socialist Republics.
Ctibor Blattny, Institute of Phytopathology, Prague-Dejvice, Sadova, Czechoslovakia.
K. N. Curtis, Cawthron Institute, Nelson, New Zealand.
Mario Curzi, Crittogamica di Pavia, Pavia, Italy.
V. Ducomet, Botany and Plant Pathology, Department National School of Agriculture, Grignan, France.
R. E. Fore, Division of Drug and Related Plants, United States Department of Agriculture and Oregon Experiment Station, Corvallis, Oreg.
Edmond Gain, University of Nancy, Nancy, France.
R. Hampp, Freising, Bayern, Germany.
J. D. Harlan, New York (State) Agricultural Experiment Station, Geneva, N. Y.
Instituut voor plantenveredeling, Wageningen, Netherlands.
R. Kirchner, Hop Experimental Institute, Vienna, Austria.
V. E. Kovalevich, Union of Soviet Socialist Republics Scientific Researching Station of Hop Growing, Shitomir, Union of Soviet Socialist Republics.
S. O. Kulezynski, Botanical Garden, Lwow, Poland.
W. Lang, Landes Anstalt für Pflanzenschutz, Hohenheim, Germany.
E. I. McClennan, Botany Department, University of Melbourne, Victoria, Australia.
R. Muck, Saaz, Czechoslovakia.
Petricek Cooperative Hop Society, Zalee, Yugoslavia.
E.S. Salmon, South Eastern Agricultural College, Wye, Kent, England.
U. Simoens, Service des Agronomes de I’Etat, Ypres, Belgium.
F. Zattler, Bavarian National Institute for the Cultivation and Protection of Plants, Munich, Bavaria, Germany.

[NOTES & FOOTNOTES]

1.  Previously in charge of hop-breeding investigations. The author is indebted to G. R. Hoerner, agent, Division of Drug and Related Plants, for collaborating on some parts of this paper dealing with pathology, and to Frank Rabak, associate biochemist in the same Division, for making the chemical and physical examinations and furnishing the data in tables 1 and 6.
2.  Present commercial bales weigh approximately 200 pounds.
3.  Attention of the reader is called to the appendix at the end of this article, listing sources of information available.
4.  Italic number in parentheses refer to Literature Cited, p. 1239.
5.  Includes some Canadian Red vines.
6.  Hermaphrodites, as in animals, are individual plants developing both male and female sexual characters.  In hops such plants produce pollen and also cones.
7.  Based on a moisture-free sample.
8.  See footnote 7, p. 1230. [This is one strange note, because there IS no footnote on page 1230 and footnote 7 (see above) makes no sense with regard to sex switching. I include this note only for historical completeness. -ASC]
9.  An infectious principle not recognized as due to a particular organism, but capable of causing disease.
10.  [There is no footenote 10 in this chapter!!! It just goes from 9 to 11! -ASC]
11.  No implication is made that this list is complete, since it is based in the main on correspondence with foreign workers.