94 BREEDING CROP PLANTS 



grains on heterozygous F 2 plants and that of hulled grains on 

 heterozygous F 3 plants. Some heterozygous F 2 plants with low 

 percentages of hulled grains gave heterozygous progeny with cor- 

 respondingly low percentages. A similar behavior was obtained 

 in the progeny of heterozygous plants with high percentages of 

 hulled grains, while plants with intermediate percentages of 

 hulled grains gave heterozygous progeny with low, intermediate, 

 and high percentages in different plants. This suggests the 

 presence of a factor which affects the percentage of hulled and 

 hull-less grains of heterozygous plants. 



Pubescence. Cultivated varieties of oats differ in the amount 

 and in the presence and absence of basal hairs on each side of the 

 callus. In some crosses only one factor is involved, in others two 

 factors. In some crosses between parents which have different 

 degrees of pubescence there is an increase in the number of basal 

 hairs, and forms are obtained in F 2 which have more pubescence 

 than either parent, likewise forms which lack pubescence. Cer- 

 tain wild forms of Avena fatua carry two independently inherited 

 factors for pubescence (see Surface, 1916; Zinn and Surface, 

 1917; Nilsson-Ehle, 1908; Love and Craig, 1918c). 



Characters of Base of Lower Grain. In wild forms of Avena 

 fatua and cultivated forms of Avena sterilis there is a distinct 

 articulation at the base of the lower grain. According to Surface 

 (1916) this causes wild oats to shatter while in cultivated races of 

 saliva the grains are not easily separated from their base and do 

 riot ordinarily shatter. The FI generation of a cross between 

 A . fatua and Kherson was intermediate as regards the base of the 

 lower grain, but nearer the cultivated form, while the upper grain 

 had a base similar to the cultivated parent. Segregation in F 2 

 g^ave a ratio of wild, intermediate, and cultivated of 1:2:1. 

 This leads to the assumption of a single factor difference which 

 separates cultivated and wild in the form of the base. As has 

 been mentioned, there is strong association of many other charac- 

 ters and the wild form of the base. Love and Craig (1918c) 

 found an indication of a single factor difference for the presence 

 and absence of basal articulation but found that the yellow factor 

 inhibited the development of the wild or articulated base. 



Avena sterilis differs from other oat species in having the upper 

 grain persistent to the rachilla. The base of the lower grain 

 resembles A. fatua in its articulation. In crosses between Burt, 

 belonging to A. sterilis, and Sixty Day, the FI was intermediate 



