On the Nature of Fertilization and Sex. 181 
and gynoplasmic components of the organism. Other breeding work 
suggests, as Castle pointed out, that the sex of the sporophyte 
behaves in inheritance as though it were a unit character, obeying 
the ordinary Mendelian rules like any other unit character. 
Cytologists also have shewn that this sex is associated in certain 
animals with the occurrence of a special chromosome. If sex is 
really of the same nature as any other unit character, the factors 
for it must be carried indifferently by either kind of gamete ; and 
the hypothesis that the sex factors are so carried is supported 
by the cytological observation that the sex chromosome may be 
carried either by spermatozoid or egg-cell. 
The sex, then, of a dioecious floweiing plant would appear 
to be dependent on the presence of certain sex factors which 
behave as do other Mendelian factors in reproduction and are 
carried indifferently by either gamete. 
These sex factors cannot therefore be the agents that 
determine the nature of the gametes themselves —whether these are 
spermatozoids or egg-cells—exhibiting the features of “ active ” or 
“ passive” protoplasm. 
Thus one must postulate the existence of two sets of 
“ factors ” : 
1. Those determining the sex characters of the 
sporophyte. These are inherited according to the 
ordinary Mendelian scheme and are carried indifferently 
by either gamete, probably by the chromosomes of the 
nucleus. Such sex factors cannot determine the nature 
of the gametes—whether these are androplasmic 
(“ active ”) or gynoplasmic (“ passive.”) 
2. Those determining the character of the gametes 
themselves, whether these are androplasmic or gyno¬ 
plasmic, i.e., composed of “ active ” or “ passive ” 
protoplasm. 
Consider, now, in the light of the above, the life history of a 
simple organism, such as the unicellular green plant Chlamydomonas, 
A zygote is formed by the union of two cells functioning as 
androplasmic and gynoplasmic gametes, i.e., a portion of “ active ” 
protoplasm unites with a portion of “ passive ” protoplasm to form 
a balanced or “ symbiotic ” product. This then undergoes successive 
divisions forming a series of free cells. (In multicellular plants 
the same process occurs, but the resillting cells do not separate 
from one another). 
