266 BOTANICAL GAZETTE [APRIL 
by any measures which would tend to prevent this embryonic 
competition. 
From a careful examination of a number of species of leptospo- 
rangiate ferns, it is clear that there is a considerable period of 
enlargement of the egg following fertilization, before the zygote 
divides. It is obvious that the decisive part of the embryonic 
selection may transpire during this early period, so that most if 
not all of the zygotes are eliminated before they have undergone 
cleavage. 
A few examples may be given showing the amount of increase 
in volume during the first stages of the embryogeny, calculated 
Fic. 25.—Fern gametophyte with several embryos in competition, representing 
slightly later stage than fig. 24; A is e; enlarged; B is e, (second unicellular embryo) 
with disintegrating nucleus, collapsing as it is aborted through embryonic competition; 
€; appears to be a third collapsed unicellular embryo (?); A and BX 200, CX42. 
from micrometer measurements. The average of several fertilized 
eggs in Osmunda cinnamomea measured 6000 cubic microns, while 
the zygote of the same species after only one cleavage measured 
19,000 cubic microns. In Adiantum the diameter of the egg 
measured 17,000 cubic microns, while the two-celled zygote 
measured 65,000 cubic microns. Ina species of Pteris the fertilized 
egg measured 33,000 cubic microns or less, while the two-celled 
zygote exceeded 195,000 cubic microns. Thus it appears that 
among leptosporangiate ferns there is a definite enlargement of 
the zygote of from 200 to 500 per cent during the first cleavages. 
