no BOTANICAL GAZETTE [august 



extreme is seen in dioecious species. Various grades of sexuality 

 intermediate between these two are seen in species classed as 

 monoecious and polygamous, most striking of which are the 

 numerous instances where all grades of sexuality are to be seen 

 among the various flowers produced by a single individual. 

 Darwin (7) presents an excellent summary of these cases as 

 evidence that ''various hermaphrodite plants have become or 

 are becoming dioecious by many and exceedingly small steps" 

 (p. 181). Darwin was not directly concerned with the problem 

 of sex determination. He was seeking to discover methods and 

 principles of evolution. In his discussion of sex heteromorphism 

 he places much emphasis on the law of compensation in the utili- 

 zation of the energy at the disposal of plants, and thus gives 

 recognition to a metabolic theory of sex determination in so far 

 as it relates to the development of the floral organs. 



There has been no special dispute over the very obvious fact 

 that the condition of hermaphroditism indicates that sex differ- 

 entiation may arise through somatic differentiation. According 

 to the sex chromosome theory, however, sex in dioecious species 

 is assumed to be determined qualitatively in reduction divisions 

 and in fertihzation, and that the two sexes are hence alternative 

 and represent fundamentally irreversible conditions. In develop- 

 ing this theory, however, little attention has been paid to her- 

 maphrodites, and in view of their predominance in plants the 

 theory cannot be regarded as expressing any broad biological law. 



The recent investigations of Goldschmidt, Banta, Riddle, 

 and LiLLiE show that the sex of dioecious species is not necessarily 

 irreversible. This is especially striking, as to demonstration in 

 pedigreed cultures, in the results obtained by Banta. By means 

 of parthenogenetic reproduction he propagated races from females 

 of Simocephalus vetulus for 130 generations, getting nothing but 

 female individuals, only to have the femaleness break up in the 

 131st generation, giving males, females, hermaphrodites, and 

 many grades of intersexes. 



Turning to plants, we have such striking cases of changes of 

 sex combined with conditions of intersexuality as are recently 

 reported by Davey and Gibson (8). They have studied the sex 



