a72 BOTANICAL GAZETTE [NOVEMBER 
Other interesting facts have been brought out from the cyto- 
logical standpoint. Several investigators have worked at pollen 
sterility from this side, and though it is not my purpose to go into 
any prolonged discussion of the matter, yet it may be well to give 
a brief account of what has been done. JuEL (12), working with a 
hybrid known as Syringa chinensis, noticed that all the pollen was 
abortive and that abortion did not take place until after the forma- 
tion of tetrads. TiscHLER (13), through his research upon the 
same hybrid, and also upon hybrids of Ribes, found that pollen 
abortion seemed to take place usually after the formation of 
tetrads. He also made a study of hybrids from a Bryonia species 
cross made by CorrEns, and found that the tetrads were formed 
but that the pollen generally aborted, as did also the embryo sacs. 
He ascribes the frequent sterility of mutants, accompanied by 
irregularities similar to those of hybrids during reduction, to the 
disturbance of the idioplasm. GrrErts (14), in working out the 
cytology of Oenothera Lamarckiana of DEVriEs, determined that 
one-half of the pollen from each tetrad aborted, and also that one- 
half of the embryo sacs did not develop. BELLING (15) speaks of 
this behavior as being unique, since, as he states, “these Oenotheras 
cannot be considered hybrids.’”’ This statement is worthy of note 
when taken into consideration with views recently expressed, not 
only about Oenothera as a genus, but concerning the Onagraceae 
as a whole. Osawa (16) has recently shown that in the case of the 
Unshu (Satsuma) orange, although this is not known to be a 
hybrid, yet nearly all the pollen aborts and the abortion takes 
place only after the formation of tetrads. ; 
As can readily be seen, all these writers emphasize the fact that 
the abortion of pollen seems generally to take place only after the 
formation of tetrads. Dorsey (17) not only points out that this 
seems to be the case with the genus Vitis, but he also distinguishes 
two kinds of abortion. To quote directly: 
In the formation of sterile and fertile pollen of the grape the heterotypic 
and homotypic divisions and the division = the mucToRpOte nucleus take place 
normally. Sterile pollen in the processes in the 
generative nucleus, or arrested ‘development previous to mitosis in the micro- 
spore nucleus. When degeneration begins early after the division of the micro- 
spore nucleus, both the generative and vegetative nuclei may remain normal. 
