s<.,.t., 1921.] YASVI:- ON THE BEHAVIOR OF CHROMOSOMES 163 



chromosomes in the meiotic phase, though some authors, e. g., 

 TiscHLER emphasized the disturbance in metabolism. 



We have to distinguish the two kinds of sterility of hybrid 

 plants, i. e., the sterility of gamates and the nonviabilitj^ or abortion 

 of zygotes. 



STERILITY OF GAMATES. The egg cell of P. somniterum is fertile, 

 the pollen grain of P. orientale is normal, and the hybrids between 

 the.se two species is viable and even vigorous than the parents ; that 

 is to say, protoplasm of the male cell of P. orientale does not affect 

 the viability of that of the female cell of P. somniferum and vice 

 versa ; and the vegetative function of the zygote protoplasm is even 

 promoted. Thus we are forced to the conclusion that the degenera- 

 tion of the pollen grains of P^ plant is due to the abnormal 

 distribution of chromosomes, which actually take place in the meiotic 

 division, and the consequent inadequate ' idic combination ' (Fujif, 

 1920) of the nucleus of the pollen cells. Eleven halves of ' somniferum 

 gemini ' as well as 21-halves of ' orientale gemini ' will form viable 

 gamates ; but only 11 out of 21 halves of the latter will be probably 

 incomplete to form a viable gamate. It follows then that 11 halves 

 of ' somniferum gemini ' is not probably equivalent each to each with 

 those 11 halves of ' orientale gemini '; and the interchange of 

 chromosomes between these two sets to form a pollen cell nucleus in 

 the process of meiosis will naturallj' produce inadequate or non-viable 

 chromosome sets to form gametic nuclei and this tendency will be 

 greater, the more of univalent chromosomes happen to be dropped off 

 in the formation of the latter. 



NONVIABILITY OF ZYGOTES. A small number of ripe seeds 

 in the capsule, is probably due to a large number of nonviable unions 

 from various kinds of gamates, and this is the main cause of the 

 abortion of z\'gotes. 



There is besides one thing to be considered, however, regarding 

 the cause of the abortion of zygotes ; that is the fact of sterility of P. 

 orientale, the d' parent. In 1919, seven flowers of P. orientale were 

 selfed, but onh- one capsule produced ripe seeds. In 1921 about 30 

 flowers of the S^ plants from the 1919 seeds were selfed, but no 

 capsule formed ripe seeds. In face of the facts of the regularit}- of 

 the meiotic process, which is nearlj' certain from the figures by 

 Tahara and of the normal developmfnt of good pollen grains, we 

 can hardly suppose the sterility of the male gamates. Although I am 

 not in a position yet to give any decisive account about the 



