INHERITANCE IN THE BARLEY SPIKE. 5 



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 Avas 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 deficiens. 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. 



