Ilo 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 fertilization, 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 GorpscHmipt, BANTA, RIDDLE, 
and Lit. 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. oe 
Turning to plants, we have such striking cases of changes of 
sex combined with conditions of intersexuality as are recently 
reported by Davey and Gipson (8). They have studied the sex — 
