196 Plant Genetics 



We have a suggestion of the same sort of behavior in 

 the case of begonias. Gardeners claim that in Begonia 

 one can secure female flowers by pinching off the male 

 inflorescences, female inflorescences developing later in 

 the same place. One gardener, at least, has been prac- 

 ticing this remarkable process for some years. 



In concluding this brief survey of sex determination 

 in plants it is obvious that some of the evidence points 

 to the sex chromosome theory, while other evidence 

 points to some physiological theory. It is perhaps best 

 at this time to conclude that one theory holds for 

 certain cases and the other theory for other cases. 



This topic should not be left without mention of the 

 classic experiments of Correns and Shull. Coreens 

 (4) crossed the dioecious Bryonia dioica with the her- 

 maphroditic B. alba, while Shull (12) crossed Lychnis 

 dioica with hermaphroditic mutants from the same. 

 The sexual behavior of the progenies in the two cases 

 was not identical, but both suggested a sex chromosome 

 theory, with the male heterozygous for sex. The theo- 

 retical explanations are so complex and dubious that they 

 cannot be conveniently discussed here; but the experi- 

 ments themselves represent a very significant type of 

 work. 



1. Allen, Charles E., A chromosome difference correlated with 

 sex differences. Science 46:466-467. 1917. 



2. Blakeslee, a. F., Sexual reproduction in the Mucorineae. 

 Proc. Amer. Acad. 40:205-319. 1904. 



, Differentiation of sex in thallus gametophyte and 



sporophyte. Bot. Gaz. 42:161-178. 1906. 



3. BuRGEFF, H., tlber Sexualitat, Variabilitat, und Verebung 

 bei Phycomyces nitens. Ber. Deutsch. Bot. Gesell. 30:679- 

 685. 1912. 



