Aug. 6, 1917 



Studies on Oat Breeding 



305 



seminaked condition. Including, then, these plants in the group of 

 plants with pubescence at the base of the lower grain, we obtain the 

 ratio of 578 pubescent to 47 smooth. The expectation on a 15-to-i ratio 

 is 586.5 to 39.1. The agreement between the observed and expected 

 numbers is fairly good and bears out the conclusion regarding the bifac- 

 torial character for pubescence found above for the selected group of 

 completely and almost completely hulled forms. This group then ap- 

 pears to represent a random sample of the F2 population in respect to 

 pubescence. To avoid the disturbing influence of the naked or semi- 

 naked condition, only this group of completely or almost completely 

 hulled forms will be considered in the further discussion. 



It will next be of interest to see whether there is any relation between 

 the genes for pubescence at the base of the lower grain and the color 

 genes. Of the 323 plants to be considered, 236 are black and 87 white. 

 This is a very close approximation to the expected 3-to-i ratio, and 

 shows that in respect to grain color this selected group of plants is rep- 

 resentative of the complete Fj generation. 



If there is no linkage between either of the factors for pubescence and 

 the color genes, the expected ratio will be 45 black pubescent to 3 black 

 smooth, to 15 white pubescent to i white smooth. The expected num- 

 bers calculated from this ratio, together with the observed number of 

 plants in each class, are shown in Table VI. 



Table VI. — Relation of the color genes and the genes for pubescence at base of the lower 



grain 



This is a very reasonable agreement between the observed and expected 

 numbers. These results show that the color genes segregate independ- 

 ently of the two genes for pubescence. 



As shown in Plate 46, A, the pubescence on the Victor oat is quite long, 

 in fact much longer than the hairs found at the base of most cultivated 

 oats. Nilsson-Ehle (4) has stated that the long and short pubescence at 

 the base of the grain segregates in a monohybrid ratio. This is found to 

 be the case in the present cross. Out of the 300 pubescent plants 217 

 have long pubescence and 83 short. This is undoubtedly a 3-to-i ratio. 



Furthermore, the genes for long and short pubescence segregate inde- 

 pendently of the color genes, as shown in Table VII. 



