130 BOTANICAL GAZETTE [AUGUST 
“anabolic habit”? induced by conditions favoring constructive 
processes (GEDDES and ‘THOMSON 10). 
The physical basis for different metabolic activity is to be 
sought in qualitative or quantitative differences; the same kind 
of substance may be involved quantitatively or different sub- 
stances may be involved either qualitatively or quantitatively. 
The recent theory of the sex chromosome is in one aspect a 
metabolic theory in which different amounts of chromatin material 
in the nucleus may be considered as affording a physical basis 
for quantitative and perhaps qualitative metabolic differences. 
The theory fails as a broad biological law in not applying to the 
conditions of hermaphroditism as already discussed, and also in 
assuming that in dioecious species there is a determination of 
sex at the time of fertilization that is exclusive for the zygote. 
As intersexuality reveals, sex in zygotes of dioecious species is 
not necessarily irreversible (see especially RippLE and LILLIE); 
and experimental work has shown (see especially RippLE) that 
the distribution of sexes among the offspring may be controlled 
in a measure which breaks up the chromosomal correlation. 
Most noteworthy of the more recent experimental data bearing 
on the chemical nature of sex determination are the results of 
Rippie. He has shown that in the pigeon “the male sex is an 
expression of metabolism at a higher level, the female sex of me- 
tabolism at a lower or more conservative level’’ (22, p. 322). The 
chemical nature of the eggs produced by a single female mated 
with a male is found to be subject to change according to whether 
egg production is forced or otherwise, and sex can thus be con- 
trolled. The physical basis for differences in metabolic activ- 
ity is to be found in changes in the chemical organization and 
relations of the food substances. That such changes can readily 
occur is quite in harmony with well known facts as to the chemi- 
cal differences in metabolic substances produced by an organ 
under different conditions. In the case of sex control in the pigeons 
it appears that it is not the amount of one or more kinds of 
food substances, but the different chemical nature of them, induced 
by the condition of the mother, that leads to differences in metab- 
olism which determine the sex of the offspring. 
