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 UNITED STATES DEPARTMENT OF AGRICULTURE 
 BULLETIN No. 869 
 
 Contribution from the Bureau of Plant Industry 
 WM. A. TAYLOR, Chief 
 
 Washington, D. C. 
 
 PROFESSIONAL PAPER 
 
 September 30, 1920 
 
 THE INHERITANCE OF THE LENGTH 
 
 OF INTERNODE IN THE RACHIS 
 
 OF THE BARLEY SPIKE 
 
 By 
 
 H. K. HAYES, Head of Section of Plant Breeding, Division of 
 Agronomy and Farm Management, College of Agriculture, Uni- 
 versity of Minnesota, and HARRY V. HARLAN, Agronomist in 
 Charge of Barley Investigations, Office of Cereal Investigations 
 
 CONTENTS 
 
 Page 
 
 Scope of the Experiments 1 
 
 Historical Review 1 
 
 Pure-Line Varieties Used in These 
 
 Studies 3 
 
 Reliability of Experimental Methods . . 4 
 Effects of Environment and Varying 
 
 Sources of Seed on Density .... 5 
 
 Purity of Parental Forms ...... 5 
 
 Inheritance of Length of Internodes in 
 
 Crosses between Pure Lines .... 9 
 
 Summary of Results 20 
 
 Discussion of Results 21 
 
 Conclusions 24 
 
 Literature Cited 25 
 
 WASHINGTON 
 GOVERNMENT PRINTING OFFICE 
 
 1920 
 
OCT 
 
 •f 3* 
 
 21 mm 
 

 UNITED STATES DEPARTMENT OF AGRICULTURE 
 
 I BULLETIN No. 869 
 
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 Contribution from the Bureau of Plant Industry 
 WM. A. TAYLOR, Chief 
 
 jrLr?"«£7L 
 
 Washington, D. C. 
 
 PROFESSIONAL PAPER 
 
 September 30, 1920 
 
 THE INHERITANCE OF THE LENGTH OF INTER- 
 NODE IN THE RACHIS OF THE BARLEY SPIKE. 
 
 By H. K. Hayes, Head of Section of Plant Breeding, Division of Agronomy and Farm 
 Management, College of Agriculture, University of Minnesota, and Harry V. Har- 
 lan, Agronomist in Charge of Barley Investigations, Office of Cereal Investigations. 
 
 CONTENTS. 
 
 Scope of the experiments 
 
 Historical review 
 
 Pure-line varieties used in these studies 
 
 Reliability of experimental methods 
 
 Effects of environment and varying sources 
 
 of seed on density 
 
 Purity of parental forms 
 
 Page. ] Page. 
 
 1 | Inheritance of length of internodes in crosses 
 
 1 between pure lines 9 
 
 3 Summary of results 20 
 
 4 Discussion of results 21 
 
 Conclusions 24 
 
 Literature cited 25 
 
 SCOPE OF THE EXPERIMENTS. 
 
 In 1915 a series of studies on the inheritance of the length of 
 internode in the rachis of the barley spike was begun in cooperation 
 with the Minnesota Agricultural Experiment Station. Internode 
 length is a particularly favorable character for such investigations, 
 as a large number of varieties furnish many gradations in internode 
 length and in a pure line the average internode length of the rachis 
 varies comparatively little from year to year. 
 
 The project was undertaken for two main reasons, (1) as a study 
 of inheritance in an unusually favorable size character and (2) as a 
 contribution to the question of the taxonomic value of the length of 
 internode of the rachis. 
 
 HISTORICAL REVIEW. 
 
 The length of internode is frequently referred to as density, and 
 both terms are used in this bulletin. As far back as Linnaeus, species 
 were differentiated by this character. With fertility, it has been, 
 consciously or unconsciously, one of the main bases of classification 
 
 182694°— 20— Bull. 869 1 
 
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2 BULLETIN 869, U. S. DEPARTMENT OF AGRICULTURE. 
 
 of most of the modern taxonomists as well. The groups of Schuebler 
 (22) 1 , Seringe (23), Heuze" (11, 12), Voss (25), Koernicke (13, 14, 15, 
 16, 17), Atterberg (2, 3, 4), and Beaven (5) involved variations in 
 density. In 1918 Harlan (10) offered an arrangement which elim- 
 inated the question of density from the major groups. It was re- 
 tained as a minor distinction only, because of the volume of the liter- 
 ature in which it had been used. Its complete elimination would 
 have left too little connection between the author's scheme and the 
 previous usage. 
 
 In classifying barleys, density is an obvious and attractive char- 
 acter. When confined to type forms the separations are ideal, but, 
 as with many things in taxonomy, its perfection depends on limited 
 material. The more material that is assembled the more the sub- 
 divisions of density have to be increased. Linna?us (18) used the 
 name Hordeum distichon to designate the lax 2-rowed and H. zeo- 
 criton to designate the very dense 2-rowed forms. Schuebler divided 
 H. disticlion into erectum and nutans. Eriksson (S) used genuinum 
 and patens to designate lax and dense subdivisions of erectum. 
 Linnaeus recognized Jiexasticlium and vulgar e as the dense and lax 
 groups of 6-rowed barleys. Koernicke divided hexasticlium into 
 pyramidatum and paraUelwm and recognized hrachyurum and macro- 
 terium of Alefeld (1) as dense and lax subdivisions of pyramidatum. 
 The finer the groups were made, the more confusing became the dis- 
 tinctions. The confusion indicated that, while there might be some 
 genetic distinctions, from a taxonomic standpoint there was no clear 
 separation. 
 
 In the mode of inheritance the situation is also complicated. As 
 a size character, the accounts are quite favorable as to its constancy, 
 and some varieties are traceable for centuries by this character alone. 
 In recent times Blaringhem (7), possibly following the lead of the 
 Svalof station, made quite elaborate studies of barley density in 
 France. Harlan (9) found density to be quite a stable character. 
 Regarding the mode of inheritance, the studies, however, are largely 
 unsatisfactory. The taxonomic papers contain no comprehensive 
 measurement of density. Many of the inheritance papers are equally 
 inadequate. In many instances fertility and density are treated 
 together, as by Von Tschermak (24). Density has been regarded 
 as recessive by Blaringhem (7) and as dominant by Von Tschermak. 
 
 The only paper which is directly concerned with the method of 
 study used in this article is that of Biffen (6), who obtained results 
 closely parallel to those presented herein. In three crosses to which he 
 paid particular attention, Biffen found the F 1 generation to be slightly 
 more dense than the lax parent, although the numbers of individuals 
 in Fj were small. The F 2 generation consisted in each case of plants 
 
 1 The serial numbers in parentheses refer to "Literature cited," at the end of this bulletin. 
 
INHERITANCE IN THE BARLEY SPIKE. 3 
 
 with spikes as lax or as dense as those of the parents, with a series 
 lying between these extremes which could not be satisfactorily classi- 
 fied without further test. In some crosses the F 2 generation curves 
 plotted from the measurements showed two peaks and in others three. 
 In a cross of zeocriton X nutans groups of plants were centered about 
 internode lengths of 2.2 and 3 millimeters, respectively. The 65 
 plants constituting the more dense group were tested in the F 3 
 generation by seeding all individuals with internode lengths ranging 
 from 1.8 to 2.6 millimeters. Of these 65 plants, 55 proved homozy- 
 gous and 10 were heterozygous. Thus, 55 out of a total of 209 plants 
 grown in F 2 bred true for densities near that of the dense parent, or 
 a close approximation of a 1 : 3 ratio. No genetic analysis is given of 
 crosses which appear to have three groups in F 2 , or lax, dense, and 
 intermediate forms. 
 
 Study has been made of the inheritance of density in wheat and, 
 although apparently pertinent, it is not comparable to one made in 
 barley, for the reason that the dense wheats are clubbed at the tip 
 and thus introduce a condition which makes comparison difficult. 
 Gradations were found in F 2 between the parents. Nilsson-Ehle (20) 
 explained these on the basis of two kinds of factors, a positive factor 
 for compactness which partially inhibited the action of one or more 
 lengthening factors. Parker (21), in a more extensive study in which 
 the statistical method was used, concludes that numbers such as 
 Nilsson-Ehle used were inadequate to demonstrate his hypothesis. 
 In Parker's studies segregation occurred in F 2 , but it seemed impos- 
 sible to determine the number of factors involved. 
 
 PURE-LINE VARIETIES USED IN THESE STUDIES. 
 
 With the exception of the Jet variety, the pure lines used in crosses 
 in the studies here reported are quite typical representatives of the 
 three degrees of density much used by taxonomists in the 6-rowed 
 barley. Their relationships are most easily made apparent by use of 
 the taxonomic key which follows. The variations in density are well 
 shown in Plate I. 
 
 KEY TO BARLEY VARIETIES USED IN DENSITY STUDIES. 
 
 Hordeum vulgare pallidum (6-rowed, hulled, awned, white). 
 
 Subvariety typica, spike lax, pure-line Manchuria. 
 
 Sub variety parallelum, spike dense, pure-line Reid Triumph. 
 
 Subvariety pyramidatum, spike very dense, pure-line Pyramidatum. 
 Hordeum distichon palmella (2-rowed, hulled, awned). 
 
 Subvariety nutans, spike lax, pure lines Hanna and Steigum. 
 
 Subvariety erectum, spike dense, pure-line Svanhals. 
 
 Subvariety zeocriton, spike very dense, pure-line Zeocriton. 
 
 Jet is a naked, black, 2-rowed barley of about the same spike 
 density as Steigum. Although Hanna and Steigum belong to the 
 same group, Steigum is slightly more dense than Hanna. Dejiciens 
 
4 BULLETIN 869, TJ. S. DEPARTMENT OF AGRICULTURE. 
 
 was not used in any of the crosses, but is included because of an 
 inherited variation found in it. The form used is lax and differs 
 from nutans in having only rudiments of lateral florets. 
 
 RELIABILITY OF EXPERIMENTAL METHODS. 
 
 In this investigation the feasibility and accuracy of density deter- 
 minations were tested in many ways. The length of internode was 
 computed from the measurement of 10 internodes in the middle, of 
 the spike. All measurements were taken in millimeters. 
 
 To test the observational accuracy, the populations from wnich the 
 density of three parents was determined were remeasured after a lapse 
 of three weeks. The difference in the measurements of Manchuria 
 was 0.02 ±0.01 mm.; of Zeocriton, 0.04 ±0.01 mm.; and of Hanna, 
 0.12 ±0.02 mm." Differences as small as 0.2 mm. in means of varie- 
 ties, therefore, can not be demonstrated by the method used. As 
 seasonal fluctuations in the means often are as great as this, the 
 method of taking the data is sufficiently accurate. 
 
 The internode measurement was taken in the middle of the spike, 
 not only because of the greater convenience, but because experiments 
 indicated that the internodes in this zone are less variable than in 
 other parts of the spike. Measurements were taken in different parts 
 of the spike on approximately 100 plants of each of the Zeocriton, 
 Pyramidatum, Manchuria, and Hanna parents. Where the spikes 
 were long enough, six different sections were measured, i. e., nodes 
 1-11, 3-13, 5-15, 7-17, 11-21, and the last 10 internodes toward the 
 tip. In Pyramidatum the measurements for nodes 7-18 and 11-22 
 could not be made. The means for these measurements, in milli- 
 meters, were as follows: Zeocriton, 1.37, 1.47, 1.66, 1.81, 1.95, and 
 2.15; Pyramidatum, 1.98, 2.12, 2.17, and 2.15; Manchuria, 2.88, 
 3.13, 3.35, 3.42, 3.36, and 3.38; Hanna, 3.90, 4.17, 4.40, 4.47, 4.35, 
 and 3.90. 
 
 The Zeocriton is the only variety in which there is a progressive 
 increase in internode length from the base to the tip. If the factor 
 or factors determining this progressive increase segregate in a normal 
 way, the progeny of a cross between this type and one in which this 
 peculiarity is absent or less pronounced, as in Pyramidatum, might 
 contain types easily misinterpreted. The mean of a pure recessive 
 for a main density factor might easily differ by 0.2 to 0.4 mm. from 
 the parent, due to the gain or loss of this marked progressive increase 
 of internode length found in Zeocriton. 
 
 Contrary to results previously reported by Harlan (9), no change 
 in internode length due to the presence of sterile nodes was observed. 
 
Bui. 869, U. S. Dept. of Agriculture. 
 
 Plate I. 
 
Bui. 869, U. S. Dept. of Agriculture. 
 
 PLATE I I . 
 
INHERITANCE IN THE BARLEY SPIKE. 
 
 EFFECTS OF ENVIRONMENT AND VARYING SOURCES OF SEED ON 
 
 DENSITY. 
 
 Wide differences of condition, such as obtain in California as com- 
 pared with Minnesota, are. sufficient to modify the expression of 
 density. As will be seen by referring to Table I, the annual fluctua- 
 tions of density measurements in a pure variety are not sufficient in 
 Minnesota to introduce any large error in the conclusions, especially 
 when it is considered that progeny are compared only with parents 
 of the same year's growth. 
 
 In 1918 there was an opportunity to test the effect of vigor of plant 
 on density. One section of the nursery produced Manchuria plants 
 which averaged 110 centimeters in height, while the same strain in 
 another part of the nursery averaged only 82 centimeters. A similar 
 difference was apparent in Svanhals. The internode lengths of the 
 Manchuria plants were 3.36 ±0.01 and 3.33 ±0.01 mm., respectively, 
 and of Svanhals, 2.56 ±0.01 and 2.65 ±0.01 mm., respectively, both 
 being within the limits of observational accuracy. 
 
 Sometimes the F x generation of a cross was grown in the Washing- 
 ton greenhouse and the seed from it was still rather immature when 
 sown in Minnesota. Plants of Manchuria from greenhouse seed gave 
 a mean internode length of 3.22 ±0.02 mm., as compared with 
 3.34 ±0.02 mm. in plants from field-grown seed. In Svanhals, the 
 difference was less, 2.49 ±0.02 as compared with 2.52 ±0.01 mm. 
 Neither variation is large enough to have any particular significance 
 in this study. 
 
 PURITY OF PARENTAL FORMS. 
 
 The variation which may be expected in a pure line within a single 
 season and from season to season is shown in Table I. The 6-rowed 
 varieties gave about the same mean average length of internode in 
 all three seasons. With the 2-rowed varieties there was more seasonal 
 fluctuation in average density. All varieties of this group gave a 
 higher mean length of internode in 1918 than in 1917. In Steigum 
 the seasonal difference reached its maximum of 0.51 ±0.03 mm., 
 and in Hanna the seasonal variation also was large. Individuals 
 of different densities in the different varieties were selected as 
 parents. The only possibility of inherited variation within the same 
 variety occurred in dejiciens. The progeny of plant 333-5-1 is sig- 
 nificantly lower in mean density. Only two or three, deficiens types 
 have been grown in the nursery, and the progeny showed no evidence 
 of hybridization. As the chance of mixture or accidental crossing 
 is small, it might be interpreted that we had chanced to select a spike 
 in which a sudden change in the factors for density had taken place. 
 
BULLETIN 860, U. S. DEPARTMENT OF AGRICULTURE. 
 
 
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INHERITANCE IN THE BARLEY SPIKE. 9 
 
 INHERITANCE OF LENGTH OF INTERNODES IN CROSSES BETWEEN 
 
 PURE LINES. 
 
 Each cross studied has been considered as a separate family. 
 For convenience, the data from each such family will be discussed 
 separately. In considering crosses, statements will be made as to 
 the number of homozygous and heterozygous forms. Such state- 
 ments can be only relative. Using the variability of the pure lines 
 as a standard, it is assumed that progeny lines of low variability are 
 homozygous, while those ot high variability are heterozygous. There 
 is no reasonable doubt of the classification of the extremes, but there 
 is a borderland where the most varying homozygotes may be in doubt. 
 
 FAMILY MANCHURIA (360) X SVANHALS (458). 
 
 The actual F x generation of the cross between Manchuria and 
 Svanhals, which was the basis of later generations discussed in this 
 bulletin, was grown in 1915. A considerable number of crosses 
 between these same pure lines of Manchuria and Svanhals were made 
 in 1917 in the greenhouse at Washington, D. 0. The data for the F t 
 reported in Table II (sec. A) are from this greenhouse seed. On the 
 basis of the coefficient of variability, this F t generation proved 
 no more variable than the parents. 
 
 In 1917 the mean average density in millimeters of the Svanhals 
 parent was 2.53 ±0.01 mm.; of the Manchuria, 3.34 ±0.01 mm.; and 
 of the F ly 2.70 ±0.01 mm. There is almost a complete dominance of 
 the dense over the lax form. 
 
 An F 2 generation was grown both in 1916 and in 1918. The means 
 for these two F 2 generations were 2.94 ±0.01 and 2.96 ±0.02 mm., 
 respectively. The variation as determined by the frequency distri- 
 bution and the coefficient of variability was much greater in F 2 than 
 in F x or in the parental forms, the coefficient of variability of the Fj 
 generation being 6.30 ±0.30 mm. and of the F 2 generations of 1916 
 and 1918, 10.20 ±0.27 and 11.82 ±0.48 mm., respectively. 
 
 Thirty-two F 3 lines, representing all F 2 types of density, were 
 grown. Thirteen of these F 2 plants appeared to give homozygous 
 progeny in the F 3 generation. The writers recognize that too few 
 plants were grown in F 3 to determine with certainty which forms 
 were homozygous. Eight of these 13 lines were continued in F 4 , and 
 five of these appeared to be homozygous. These results show that a 
 considerable number of the F 2 plants selected bred true in F 3 , although 
 no conclusion as to the actual percentage can be made. 
 
 The five types which proved to be homozygous in F 4 gave mean 
 densities as follows: 378-1, mean 2.57 ±0.01 mm.; 378-11, mean 
 2.64 ±0.01 mm.; 378-14, mean 3.37 ±0.02 mm.; 378-23, mean 2.55 ± 
 0.01 mm.; 378-31, mean 2.58 ±0.01 mm. Selection 378-88 gave the 
 highest coefficient of any third-generation line. Two heads were 
 selected which bred true in F 4 for densities near the Manchuria parent. 
 182694°— 20— Bull. 869 2 
 
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.INHERITANCE IN THE BARLEY SPIKE. 15 
 
 The Svanhals parent gave a mean of 2.71 ±0.01 mm. and the 
 Manchuria one of 3.46 ±0.01 mm. in 1918. No sorts were obtained 
 which were homozygous for densities very different from those of 
 the parents. 
 
 FAMILY MANCHURIA (360) X STEIGUM (17). 
 
 The parental forms of the Manchuria and Steigum cross gave 
 nearly the same average density in 1916. In 1918 the Manchuria 
 parent gave about the same average density as in 1916, but the 
 Steigum averaged somewhat higher than in the previous year. The 
 coefficient of variability of the Manchuria parent in 1917 was 4.19 ± 
 0.15 mm.; of the Steigum parent, 4.90±0.17 mm.; and of the F 2 gen- 
 eration which was grown in 1916, 7.69 ±0.21 mm. The data are 
 reported in Table II (sec. B). 
 
 As Table II shows, some forms bred true in F 3 and in F 4 , while 
 others were as variable as the F 2 generation. Selection 368-22 in 
 the F 3 and F 4 generations gave means of 3.21 ±0.02 and 3.29 ±0.01 
 mm., respectively. When compared with the parental forms, it 
 seems that we have here a lower density line than either parent. As 
 the number of individuals is small in many F 3 lines, it does not seem 
 profitable to analyze more closely the results obtained. 
 
 FAMILY PYRAMIDATUM (476) X JET (454). 
 
 Table II (sec. C) shows that the parental forms of the cross between 
 Pyramidatum and Jet are of very different densities. The Pyrami- 
 datum parent gave a mean density of 2.11 ±0.01 mm. in 1918; 
 the Jet, 3.92±0.01 mm.; while the F x generation averaged 2.86±0.01 
 mm. The F t generation is, therefore, slightly more dense than the 
 parental average, which is 3.01 mm. This is quite different from the 
 F x generation in the cross between Manchuria and Svanhals, in which 
 there was an almost complete dominance offline dense over the 
 lax form. / 
 
 The F 2 generations were grown both m^J&lG and in 1918. The 
 means for these two F 2 generations were about the same as the 
 parental average, being 2.92 ±0.04 mm. and 3.10 ±0.03 mm., respec- 
 tively. The highest coefficient of variability for the Jet parent is 
 6.93 ±0.39 mm., while the highest coefficient for Pyramidatum is 
 6.16 ± 0.21 mm. The coefficients of variability for the two F 2 genera- 
 tions are 16.44 ±0.87 mm. and 18.38 ±0.81 mm., respectively, while 
 the frequencies of the F 2 generations range from above the modal 
 class of the lax parent to the modal class of the dense parent. It is 
 of interest to note that with a total of 87 Fi plants, none were of the 
 same frequency range as that of the parents, all being of intermediate 
 density. Of the 22 F 2 plants continued in F 3 , ten would have been 
 included within the limits of this F x population. Of these ten, eight 
 gave about as variable a progeny as the F 2 generation, while two 
 
16 BULLETIN 869, U. S. DEPARTMENT OF AGRICULTURE. 
 
 appeared to give homozygous dense progeny. Of the entire 22 
 plants, representing all types of F 2 densities, nine proved about as 
 variable in F 3 as the F 2 generation. 
 
 Seven F 3 selections which appeared to be breeding true, as deter- 
 mined by the frequency distribution and coefficient of variability, 
 were tested in the F 4 generation. This was done by selecting 10 heads 
 of different densities and growing the progeny of each separately. 
 Where all heads gave similar results, they are combined in the table 
 and are given as the result of 10 plants. 
 
 The F 3 line 325-5, of which only 26 plants were available for study, 
 gave a mean of 3.15 ±0.02 mm. in 1917, with a low coefficient of 
 variability. On testing this line in 1918, when data from 213 plants 
 were available, a somewhat higher mean was obtained, or 3.43 ±0.01 
 mm. Its coefficient of variability is also somewhat larger than in 
 the homozygous parental forms. Selection 325-15 proved pure in 
 F 4 with the exception of the progeny of one plant which gave as 
 great a variability as the F 2 generation. Why one plant should 
 behave so differently from the nine others is difficult to explain. 
 The possibility of a natural cross must not be overlooked, although 
 observations show that these are very infrequent. An occasional 
 error is also a possibility, although precautions, were taken to elimin- 
 ate these as far as possible. 
 
 The F 4 means for the seven lines which gave evidence in F 3 and F 4 
 indicating that they were homozygous are as follows: 325-5 (10 
 plants), 3.43 ±0.01 mm.; 325-13 (10 plants), 3.47 ±0.01 mm.; 
 325-16 (9 plants), 3.74 ±0.01 mm.; 325-18 (10 plants), 2.24 ±0.01 
 mm.; 325-20 (10 plants), 2.47 ±0.02 mm.; 325-21 (10 plants), 
 3.95 ±0.01 mm.; 325-22 (10 plants), 3.72 ±0.01 mm. 
 
 Of these, five have mean densities which are not very different 
 from that of the Jet (lax) parent, while the means of the other two 
 are similar to that of the Pyramidatum parent. The most dense 
 and the least dense of the five lax homozygous segregates have mean 
 internode lengths of 3.43 ± 0.01 mm. and 3.95 ± 0.01 mm., respectively. 
 As great a difference as this in any one season would not be expected 
 in a sort homozygous for similar characters. It is not much greater, 
 however, than seasonal variation in the means of several of the pure 
 2-rowed forms, which seem more susceptible to such variability 
 than the 6-rowed parents. Inheritance of such a reaction difference 
 might possibly explain the results here represented. Whatever expla- 
 nation may be given for these new means, here, as in the Man- 
 churia X Svanhals cross, no homozygous forms were produced 
 which differed materially in density from the density of one or the 
 other parent. 
 
INHERITANCE IN THE BARLEY SPIKE. 17 
 
 FAMILY HANNA (460) X REID TRIUMPH (404). 
 
 The parental forms, Hanna and Reid Triumph, are of distinctly 
 different densities, and there is no overlapping of frequency distri- 
 butions during the three years in which they have been grown. In 
 Table II (sec. D) the mean of the Hanna parent ranges from 
 4.12±0.02 mm. in 1916 to 4.56±0.01 mm. in 1918. The Reid 
 Triumph variety has much less seasonal variation, the mean in 1917 
 being 2.73 ±0.01 mm. and in 1916, 2.64 ±0.01 mm. It is of interest 
 to note that the Reid Triumph has about the same average mean as 
 the Svanhals 2-rowed form, while the Hanna is considerably more 
 lax than the Manchuria form which was crossed with the Svanhals 
 variety. 
 
 The F 2 generation of the cross between Hanna and Reid Triumph 
 proved more variable than the parents and frequently gave distri- 
 bution from below the mode of the Reid Triumph to considerably 
 above the mode of the Hanna parent. Twenty F 2 plants were grown 
 in F 3 , some giving as variable a population as obtained in F 2 , while 
 other F 3 lines were no more variable than the parental forms. 
 
 Fourteen of these F 3 lines which gave the clearest indication of 
 being homozygous were further tested in the F 4 generation. The 
 method was similar to that previously used, 4 to 10 plants of a line 
 being grown and the combined result being the basis of conclusions 
 as to purity. Of the 14 lines tested in F 4 , 8 gave evidence in the com- 
 bined F 3 and F 4 data to show that they are homozygous for density. 
 
 Those which are of questionable purity will be briefly considered. 
 Selection 406-3 gave a mean of about the same density as the Reid 
 Triumph parent, but the coefficient of variability is somewhat higher 
 than in the pure parental lines. Selection 406-4 proved to be 
 heterozygous. One of the head selections, 406-4-3, produced a type 
 which seems pure for density. The mean of this line is 3.72 ±0.03 
 mm. Selection 406-9 seems to be heterozygous. Probably 406-9-1 
 is homozygous, the average mean being about the same as that of 
 the Hanna parent. Selection 406-10 also is more variable than the 
 pure parental variety. The frequency distribution indicates that 
 fewer density factors are involved than in the F 2 generation. Selec- 
 tions 406-16 and 406-18 appear to be heterozygous. In later gen- 
 erations two selections of 406-18 seem to be homozygous. Thus 
 406-18-5 is probably breeding true with a mean density of 3.40 ±0.02 
 mm,, while 406-18-9 gives evidence of being homozygous for a 
 mean of 2.66 ±0.02 mm. 
 
 Those which seem nearly homozygous by an examination of their 
 frequency ranges and coefficients of variability as obtained in F 3 
 and F 4 generations are as follows: 406-1, mean 2.81 ±0.01 mm.; 
 406-5, mean 4.43 ±0.01 mm.; 106-7, mean 2.43 ±0.01 mm.; 406-8, 
 mean 4.32 ±0.01 mm.; 406-11, mean 4.32±0.02 mm.; 406-12, mean, 
 
18 BULLETIN 869, U. S. DEPARTMENT OF AGRICULTURE. 
 
 2.84 ±0.02 mm.; 406-19, mean 3.29 ±0.01 mm.; 406-22, mean 
 4.37 ±0.01 mm. 
 
 Aside from these, individual heads grown in F 4 which appear to 
 give homozygous progeny as a result of the single season's test are 
 as follows: 406-4-3, mean 3.72±0.03 mm.; 406-9-1, mean 4.30±0.04 
 mm.; 406-18-5, mean 3.40 ±0.02 mm.; 406-18-9, mean 2.66 ±0.02 
 mm. 
 
 The means for these' four F 4 families are somewhat unreliable 
 because of the small number of individuals grown. All coefficients 
 of variability, however, are very small. 
 
 These results show that homozygous intermediates may be pro- 
 duced, as well as homozygous types, which give about the same aver- 
 age density as the parental forms. No analysis of average differ- 
 ences as small as 0.2 to 0.3 mm. has been attempted. The fact that 
 environmental or other seasonal characters may modify the expres- 
 sion of a character nullifies such close analysis. 
 
 FAMILY HANNA (460) X ZEOCRITON (1039). 
 
 The Hanna used in the cross with Zeocriton is the same pure line 
 that was used in the cross with Reid Triumph. Zeocriton is a very 
 dense 2-rowed form. This cross is between the most dense and the 
 most lax form used in this study. 
 
 The F 3 generation shown in Table II (sec. E) ranged from above 
 the modal class of Hanna to the modal class of Zeocriton, even though 
 only 141 individuals were studied. It has a correspondingly high 
 coefficient of variability. 
 
 An examination of the coefficients obtained in later generations 
 show that some are as large as those obtained in the F 2 line. Others 
 are intermediate, being significantly larger than any obtained in the 
 pure forms, while still others are as small as those obtained for the 
 pure parental lines. This would indicate that the mode of inheritance 
 was more complex than in the cross between Pyramidatum X Jet 
 previously mentioned. 
 
 Selection 448-9, which was almost as variable in the F 3 as in the 
 F 2 generation, was selected for further experiment, the progeny of 
 30 plants being measured in the F 4 generation. Data from 7 of the 
 30 progeny lines are presented, as the remaining 23 all appeared to 
 be segregating. Results of density studies in F 4 lines 448-9-7, 
 448-9-14, 448-9-16, and 448-9-29 are given, as these indicate the 
 segregation obtained in the unpresented lines. No F 4 line of greater 
 coefficient of variability than 448-9-7 was obtained, and none with a 
 wider frequency range than 448-9-16. Three lines appear to be 
 homozygous, as determined by the frequency distribution and coeffi- 
 cient of variabilitv. These are shown in Table III. 
 
INHERITANCE IN THE BARLEY SPIKE. 
 
 19 
 
 Table III. — Homozygous plants of selection 448-9 of the Hanna-Zeocriton cross, F 4 
 
 generation. 
 
 Fi line. 
 
 448-9-4. 
 448-9-19 
 448-9-30 
 
 Number of 
 individuals. 
 
 Mean. 
 
 Millimeters. 
 2.06±0.01 
 3.41± .04 
 4.30± .02 
 
 Coefficient of 
 variability. 
 
 6.80±0.41 
 7.33± .87 
 4.65± .29 
 
 The mean of 448-9-19 is not as reliable as of the other two lines, 
 as only 16 individuals were available for the study. 
 
 Selections 448-7 and 448-13 appear heterozygous in the F 3 genera- 
 tion and have about the same degree of frequency range. The coeffi- 
 cients of variability are much smaller than in F 2 , but are significantly 
 larger than in the pure parental forms. The frequency range for 
 448-7, of which 39 plants were studied, was from 2.0 to 3.2 mm. 
 Two plants from each of these lines gave evidence of being homozy- 
 gous in F 4 . These are shown in Table IV. 
 
 Table IV. — Homozygous plants of selections 448-7 and 448-13 of the Hanna-Zeocriton 
 
 cross, F t generation. 
 
 F t line. 
 
 Number of 
 individuals. 
 
 Mean. 
 
 Coefficient of 
 variability. 
 
 448-7-1 
 
 107 
 102 
 64 
 57 
 
 Millimeters. 
 2. 21 ±0.01 
 3.12± .01 
 3.19± .02 
 4.15± .02 
 
 7.69±0.35 
 
 448-7-3 
 
 5.77± .27 
 
 448-13-2 
 
 6.27± .37 
 
 448-13-5 
 
 4.58± .29 
 
 
 
 Four of the 20 F 2 plants which were tested in F ? appeared to give 
 homozygous progeny. Three of these proved to be homozygous by 
 further test, while one, 448-11, proved heterozygous. The F 4 lines of 
 interest which seem to be homozygous are shown in Table V. 
 
 Table V. — Homozygous plants of selection 448-11 of the Hanna-Zeocriton cross, F 4 
 
 generation. 
 
 F t line. 
 
 Number of 
 individuals. 
 
 Mean. 
 
 Coefficient of 
 variability. 
 
 448-11-2 
 
 73 
 45 
 
 Millimeters. 
 3.08±0.01 
 3.69± .02 
 
 5.52±0.31 
 
 448-11-3 
 
 4.34± .31 
 
 
 
 The three lines of especial interest which appeared homozygous by 
 both the F 3 and F 4 study are as follows: 448-1, mean 2.30 ± .01 mm. ; 
 448-5, mean 2. 88 ±.01 mm.; 448-16, mean 4. 30 ±.01 mm. The F 4 
 generation means are given for these lines, as they are based upon 
 larger numbers than the F 3 test. Typical spikes of the parent 
 varieties and of these lines are shown in Plate II. 
 
20 BULLETIN 869, U. S. DEPARTMENT OF AGRICULTURE. 
 
 In the Hanna X Zeocriton cross there are a number of homozygotes 
 of a density intermediate between the densities of the parents. The 
 homozygotes of this cross appear to fall in groups. Three near the 
 dense parent have internode lengths ranging from 2.06 to 2.30 mm. 
 Three near the lax parent have internode lengths ranging from 4.15 
 to 4.30 mm. Four moderately dense intermediates have internode 
 lengths varying from 2.88 to 3.19 mm., and two lax intermediates 
 have internode lengths of 3.41 and 3.69 mm. This grouping is arbi- 
 trary, as the difference between the two intermediate groups is little 
 more than between individuals of either intermediate group. Some 
 homozygous intermediates from this cross have densities approxi- 
 mately the same as those of parents used in other crosses studied. 
 
 SUMMARY OF RESULTS. 
 
 - The observational accuracy is such that differences in density 
 greater than 0.2 mm. are significant when the measurements are 
 taken in the middle part of the spike. 
 
 Except in the Hanna and Steigum varieties the seasonal fluctua- 
 tions in the means of the parents were not more than 0.2 mm. The 
 seasonal variations in the means of the 2-rowed were greater than in 
 the 6-rowed varieties. 
 
 The density of the ¥ l generation does not have an unvarjmig relation 
 to the density of the parents. In the Svanhals X Manchuria cross 
 density is dominant in the F x generation. In the Pyramidatum X Jet 
 cross it was intermediate. 
 
 The two F t generations grown were no more variable than the 
 parental sorts and all crosses gave segregation hi F 2 . Although the 
 number of F 2 plants grown averaged no greater than that of the 
 parental forms, the frequency ranges extended from the modal class 
 of one parent to the modal class of the other and often beyond these 
 classes. 
 
 The F 3 generation contained progeny groups which were no more 
 variable for length of rachis internode than pure lines of the parents. 
 Rather extensive studies of a number of F 4 generations gave further 
 evidence of purity of several of these F 3 lines. 
 
 The Manchuria X Svanhals and Pyramidum X Jet crosses gave 
 forms homozygous for densities similar to those of the parents but 
 none homozygous for intermediate densities. Crosses between Hanna 
 and Reid Triumph and between Hanna and Zeocriton gave types 
 homozygous for densities intermediate between the densities of the 
 parents, as well as near those of their parents. The latter cross pro- 
 duced homozygous forms similar to Reid Triumph, Hanna, and their 
 homozygous intermediates, as well as forms like the Zeocriton parent. 
 The range of means of these homozygous forms was almost continu- 
 ous, although there was an indication of two centers of intermediate 
 
INHERITANCE IN THE BARLEY SPIKE. 21 
 
 density. More extensive study would be needed to determine whether 
 these apparent centers are of any significance. 
 
 DISCUSSION OF RESULTS. 
 
 From the fact that segregates homozygous for density are apparent 
 in the measurements of the F 3 and F 4 generations, it seems safe to 
 conclude that internode length in the barley rachis may be explained 
 on the factor hypothesis. The number or value of the factors involved 
 is not readily estimated. In a general way the results of the Man- 
 churia X Svanhals and the Pyramidatum x Jet crosses seem to 
 indicate a single main factor difference. The proportion of homo- 
 zygotes is roughly satisfactory, and the absence of homozygotes differ- 
 ing greatly from the mean of their parents is also in favor of this 
 belief. The dominance of density in the F x generation in the first 
 cross and its intermediate expression in the second is of interest. 
 
 The results in the Hanna X Reid Triumph cross in the same way 
 indicate a broad difference of two factors. In this cross forms were 
 isolated that were homozygous for intermediate densities, as well as 
 forms having densities near those of the parents. These results can 
 be interpreted very satisfactorily on the basis of two main factors 
 for internode length. These factors are cumulative in effect, both 
 being necessary to produce the extreme type. The results show that 
 a sort may be homozygous for one of the factors and heterozygous 
 for the other. At least, heterozygous forms whose progeny range is 
 from the intermediate group to one or the other parent are so 
 interpreted. 
 
 The Hanna X Zeocriton cross gave homozygous intermediates of 
 unlike value, as well as homozygous sorts which were like the parents. 
 If the presence and absence hypothesis is here used, three main 
 factors may be postulated to explain the genetic facts. These factors 
 may be supposed to be of like value, each inherited independently, 
 each allelomorphic to its absence, the number showing a hetero- 
 zygous condition being half the homozygous sorts. This hypothesis 
 explains the genetic fact fairly well. Other minor factor differences 
 are doubtless necessary to explain all of the results. One known 
 minor character of some density significance separates the parental 
 forms. This is a difference in the progressive density from the base 
 to the tip of the rachis, the Zeocriton parent being the only sort 
 which shows a constant increase in length of internode from the base 
 to the tip of the spike. 
 
 A comparison of the Pyramidatum x Jet cross with the Hanna X 
 Zeocriton cross illustrates some facts regarding the mode of inherit- 
 ance of density. These are the two widest crosses made in the study. 
 The first produced no homozygous intermediates. The second pro- 
 duced many. An F x generation was grown of the Pyramidatum X 
 
22 
 
 BULLETIN 869, U. S. DEPARTMENT OF AGRICULTURE. 
 
 Jet cross. It was of intermediate density and no more variable than 
 the parental forms. The second generation is shown in figure 1 as 
 a multimodal curve with peaks at densities corresponding to those of 
 the parents and the F x generation. The homozygous forms pro- 
 duced closely approximated the densities of the parental varieties, as 
 is illustrated by the curves. Although there is considerable varia- 
 bility in the means of the more lax segregates, this is no greater than 
 the seasonal variation of the means of several of the 2-rowed forms. 
 
 The contrast between the Pyramidatum x Jet and the HannaX 
 Zeocriton crosses is very striking. Each showed wide segregation 
 
 &o 
 
 £0 
 
 <?o 
 
 30 
 
 20 
 
 % /o 
 
 
 
 
 
 
 i 
 1 
 
 \ 
 % 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 1 
 1 
 1 
 
 \ 
 1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 1 
 
 1 
 
 » 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ( 
 
 1 
 1 
 
 
 « 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ; 
 
 
 
 
 
 
 
 
 
 
 
 
 
 -*^«. 
 
 '/v 
 
 
 
 -^ 
 
 jri 
 
 
 9 
 
 
 
 
 
 SO 
 
 3o 
 
 /.& /.& 2.0 ?.2 ?.*? 2.G 2.8 3.0 3.2 3.-4 3.& 3.3 ^.O -<?.2 <?s? -"Z6* *?.3 
 
 Fig. 1.— Diagrams showing the densities of parental forms and Fi and F 2 generations of a cross between 
 the Pyramidatum and Jet barleys (upper) and of four homozygous forms from this cross in the F 3 
 generation (lower). 
 
 in the F 2 generation. Hanna X Zeocriton, however, produced a much 
 smaller proportion of homozygous forms in F 3 and F 4 than the 
 Pyramidatum-Jet cross. Homozygous intermediates as well as forms 
 with the parental densities were produced in the F 3 generation. The 
 heterozygous lines were of different types, some being as variable as 
 the F 2 , while others were more variable than the pure forms, but less 
 so than the F 2 generation. The means of the heterozygous forms 
 were also of different values. The results are illustrated in figure 2. 
 These graphs show the parental and F 2 types and four pure F 3 forms 
 of unlike densities, as well as the heterozygous lines obtained. This 
 cross has given nearly all sorts of densities, and by this one cross the 
 different densities of the parental forms used in these experiments 
 have been again obtained. 
 
INHERITANCE IN THE BARLEY SPIKE. 
 
 23 
 
 These results show that, although density is a very stable size 
 character, in some crosses numerous factors are involved which, by 
 recombination, produce homozygous forms showing an almost con- 
 tinuous range of density from the very lax to the dense types. It is 
 only reasonable to conclude that if a greater number of varieties had 
 been studied, together with crosses between them, a continuous range 
 for the average length of internode of homozygous forms could be 
 obtained which would show only small differences in average density 
 between types. These results are of considerable interest in barley 
 classification. While dependable in the isolation and description of 
 
 C«7 
 
 20 
 
 - 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Jzcc 
 
 >cxw 
 
 3V 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 r 
 
 -/&/3 
 
 b-5? 
 
 /3/S 
 
 y 
 
 
 
 
 
 
 -- 
 
 
 
 
 
 
 
 \30 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 / 
 
 "* 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ,• 
 
 
 \ 
 
 / 
 
 / 
 / 
 
 \ > 
 
 ^ 
 
 
 
 
 
 
 
 
 
 
 
 
 \ 
 
 
 
 
 ! 
 
 
 V 
 /• 
 
 
 
 s 
 
 \ 
 \ 
 
 
 
 
 
 
 
 / 
 
 fS-/ 
 
 
 fan 
 
 \ 
 
 
 
 
 ft*S- 
 
 |\ 
 
 
 
 \ 
 
 \ 
 
 
 
 
 Fig. 2.— Diagrams showing the densities of parental forms and of the F 2 generation in a cross between 
 the Zeocrlton and Hanna barleys (upper), of four pure lines (middle), and of several heterozygous 
 lines (lower). 
 
 strains, groups founded on this character are likely to overlap and 
 ] km ice to be of limited value for taxonomic purposes. 
 
 While the general genetic results of these crosses are explained on 
 a broad factor basis of differences of one to three factors, the fact 
 remains that the homozygous segregates corresponding to the parents 
 do not always have the exact density of the parents. Likewise, the 
 forms homozygous for intermediate densities do not all fall together 
 but in groups, which, in the Hanna X Zeocriton cross become almost 
 continuous, even where limited numbers are concerned, and might 
 become wholly continuous if it were possible to carry the full number 
 to the fourth generation. Obviously, there are modifying factors, 
 and so far as they affect density they may be considered as minor 
 density factors. Several explanations are possible. These varia- 
 
24 BULLETIN 869, U. S. DEPARTMENT OF AGRICULTURE. 
 
 tions may be associated with the same variability which manifests 
 itself in seasonal fluctuations. They may be due to the differences 
 in the progressive density from the base to the tip of the rachis, which 
 is more marked in some than in other varieties. Other explanations 
 might be suggested, but in the absence of definite proof it seems 
 unwise to attempt a more detailed analysis of the results. 
 
 CONCLUSIONS. 
 
 Despite the handicaps of the investigations, a number of points are 
 established. 
 
 (1) Internode length in the barley rachis is a very stable character, 
 which is much less affected by environmental conditions than many 
 size characters. 
 
 (2) Segregation occurs in the F 2 generation of crosses, and forms 
 homozygous for density appear in this generation, their purity being 
 demonstrated in the F 3 generation. 
 
 (3) In some crosses new lines with densities differing much from 
 those of their parents can not be secured, while in others lines with 
 very different densities may be isolated. 
 
 (4) The inheritance of internode lengths may be interpreted on the 
 factor hypothesis. Some of the crosses studied apj:>eared to differ 
 by a single main factor of density, while in others two or three main 
 factors are necessary to explain the genetic results. Minor factors 
 were evident whose number or nature was not established and through 
 whose action the means of homozygous forms of intermediate 
 densities in some crosses may become more or less continuous between 
 the means of the parents. 
 
LITERATURE CITED. 
 
 (1) Alefeld, F. G. C. 
 
 1866. Landwirtschaftliche Flora . . . 363 p. Berlin. 
 Atterberg, Albert. 
 
 (2) 1889. Die Erkennung der Haupt-Varietaten der Gerste in den nordeuro- 
 
 paischen Saat-und Malzgersten. In Landw. Vers. Stat., Bd. 36, p. 23-27. 
 
 (3) 1891. Die Klassification der Saatgersten Nord-Europas. In Landw. Vers. 
 
 Stat., Bd. 39, p. 77-80. 
 
 (4) 1899. Die Varietaten und Fnrmen der Gerste. In Jour. Landw., Bd. 47, 
 
 Heft 1, p. 1-44. 
 
 (5) Beaven, E. S. 
 
 1902. Varieties of barley. In Jour. Fed. Inst. Brewing, v. 8, no. 5, p. 542- 
 593, 12 fig. Discussion, p. 594-600. 
 
 (6) Biffen, R. H. 
 
 1907. The hybridization of barleys. In Jour. Agr. Sci., v. 2, pt. 2, p. 
 183-206. 
 
 (7) Blaringhem, L. 
 
 1910. Etudes sur 1 'amelioration des cms d'orges de brasserie. 288 p., illus. 
 
 (8) Eriksson, Jacob. 
 
 1889. Collectio cerealis. Varietates cerealium in Suecia maturescentes 
 continens, fasc. 1, 10 p., 2 fig. Stockholm. 
 Harlan, H. V. 
 
 (9) 1914. Some distinctions in our cultivated barleys with reference to their 
 
 use in plant breeding. U. S. Dept. Agr. Bui. 137, 38 p., 16 fig. 
 Literature cited, p. 37-38. 
 
 (10) 1918. The identification of varieties of barley. U. S. Dept. Agr. Bui. 622, 
 
 32 p., 4 pi. Literature cited, p. 31-32. 
 Heuze, Gustave. 
 
 (11) [1872.] Les plantes alimentaires. 2 v., illus. Paris. 
 
 (12) 1896-97. Les plantes cereales. Ed. 2, 2 v., illus. Paris. 
 
 KOERNICKE, F. A. 
 
 (13) 1873. Systematische Uebersicht der Cerealien und monocarpischen Legumi- 
 
 nosen . . . 55 p., 1 tab. Bonn. 
 
 (14) 1882. Die Saatgerste. Hordeum vulgare 1. 'sensu latiere. In Ztschr. 
 
 Gesam. Brauw., Jahrg. 5, p. 113-138, 161-172, 177-186, 193-203, 205- 
 208, 304-311, 329-336, 393-413. PI. 5-14. 
 
 (15) 1885. Handbuch der Getreidebaues. 2 Bd. Berlin. 
 
 (16) 1895. Die hauptsachlichsten Formen der Saatgerste ... 15 p. Bonn. 
 
 (17) 1908. Die Entstehung und das Verhalten neuer Getreidevarietaten. In 
 
 Arch. Biontol., Bd. 2, Heft 2, p. 389-437. 
 
 (18) LlNNE [LlNN^SXTS], CARL VON. 
 
 1753. Species plantarum ... t. 1. Holmiae. 
 
 (19) Newman, L. H. 
 
 1912. Plant breeding in Scandinavia. 193 p., 63 fig. Ottawa. Literature 
 
 cited, p. 188-193. 
 
 25 
 
26 BULLETIN 869, U. S. DEPARTMENT OF AGRICULTURE. 
 
 (20) Nilsson-Ehle, H. 
 
 1909. Kreuzungsuntersuchungen an Hafer und Weizen. 122 p. Lund. 
 
 (21) Parker, W. H. 
 
 1914. Lax and dense eared wheats. In Jour. Agr. Sci., v. 6, no. 3, p. 371-386, 
 fig. 1, pi. 1. 
 
 (22) SCHUEBLER, GuSTAV. 
 
 [1818.] Dissertatio inauguralis botanica sistens characteristicen et descrip- 
 tiones cerealium in horto academico Tubingensi et in Wiirtem- 
 bergia ... 47 p., pi. Tubingae. Inaug. Diss. 
 
 (23) Seringe, N. C. 
 
 1841-42. Descriptiones et figures des cereales Europeennes. In Ann. Soc. 
 Roy. Agr. Lyon, t. 4, p. 321-384, pi. 1-9, 1841; t. 5, p. 103-196, pi. 
 2-10, 1842. 
 
 (24) Tschermak, Erich von. 
 
 1914. Die Verwertung der Bastardierung fur phylogenetische Fragen in der 
 Getreidegruppe. In Ztschr. Pflanzenziicht., Bd. 2, Heft 3, p. 
 291-312. 
 
 (25) Voss, A. 
 
 1885. Versuch einer neuen Systematik der Saatgerste. In Jour. Landw., 
 Jahrg. 33, Heft 3, p. 271-282. 
 
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