The Mode of Inheritance of Semi-Steiility in the Offspring of Certain Hyhri'i Plants. 34 ] 



niegaspores witli Kli or ki will alunt: lliosf with KL iiocaiise they 

 have abnormally two factors instead of one; and those with kl heeanse 

 they lack an indisjiensahle factor. The sperm <jametes of the Fi i)lants 

 will then he Kl and kL, and the egg gametes also Kl and klj. The F» zygo- 

 tes will l)e (I follow Castle's and Sta('Kelbki{(;'s notation i K^l,. + k.Ls 

 -\- 2 KkLI. The homozygotes have returned to the parents of the cross, 

 and are henceforward constant. The heterozygotes resemble in these 

 genetic factors the Vi plants, and are semi-sterile. On self-fertilization. 

 the same segregation occurs again. In these crosses, all the semi-sterile 

 plants are heterozygous for two factors, and uo plant is heterozygous 

 for one of these factors alone: so that in time all the semi-sterile ])lants 

 are eliminated, like any other heterozygotes under continued self- 

 fertilization. 



This hypothesis accounts for all the facts at present known. If 

 we cross at random different fertile lines from the progeny of any 

 semi-sterile plant or plants; then half the crosses should give all fertile 

 progeny, since Ki is crossed with Kl, or kL with kL; and half the 

 crosses should give all semi-sterile progeny, since Kl is crossed by kL, 

 or kL by Kl. This crucial e.\periment remains to be performed. 



I wish in concluding to express my thanks to B. F. Floyd, for 

 independent estimations of pollen-grains and embryo-sacs; and to 

 C. D. Gunn and C. W. Long, for careful work in counting seeds and 

 examining flowers. 



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