130 BOTAXICAL 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 metabohc 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 Riddle and Lillie); 

 and experimental work has shown (see especially Riddle) 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 

 Riddle. 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 metabohc 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 metabohc 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- 

 ohsm which determine the sex of the offspring. 



