BROWN: EMBRYO-SAC AND EMBRYO IN PHASEOLUS 543 
two basal cells form the suspensor and the terminal cell develops 
into the embryo proper. 
_g. The dermatogen is cut off when the embryo proper consists 
of about sixteen cells. When the suspensor consists of four rows 
of about seven or eight cells each, the two tiers of cells at its base 
become swollen and conspicuously elongated. 
10. The primary endosperm nucleus usually divides before 
the first division of the egg; two of the daughter nuclei resulting 
from the first ‘two divisions place themselves on either side of the 
young embryo; and in succeeding divisions the endosperm nuclei 
place themselves in thé peripheral region of the embryo-sac. 
11. The divisions of the endosperm nuclei may be simulta- 
neous, or nuclei in all stages of division may be found at the same 
time, from resting nuclei at one end of the endosperm to late 
telophases at the opposite end. 
12. Endosperm cells are formed in the region immediately 
about the embryo, but are later absorbed. 
I wish to express my sincere appreciation to Dr. C. E. Allen, 
who suggested this work and under whose supervision it was done. 
UNIVERSITY OF WISCONSIN 
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