OF COOPERIA DRUMMONDII 40] 
Following fertilization the endosperm nucleus divides, and by 
subsequent mitotic divisions a number of free nuclei, apparently 
without nuclear walls, are formed (Fic. 17), which are imbedded 
in the cytoplasm lining the wall of the sac and surround- 
ing the embryo. Free nuclei are found in Alisma Planiago 
(Schaffner, 10), Leucojum vernum (Hofmeister, 5), and Xyris 
indica (Weinzieher, 13). Eventually these nuclei become sepa- 
rated by cell walls, which are at first laid down so as to include 
several nuclei in each lumen (Fic. 18). Later these multinucleate 
cells divide in such a manner that a single nucleus becomes en- 
closed within a lumen. The cells divide by amitosis after the 
walls are laid down. Several cases have been noted where endo- 
sperm formation was lacking. In connection with endosperm 
development in Cooperia Drummondii the description of endo- 
sperm formation in Leucojum vernum as given by Hofmeister (5) 
is of interest: “. . . the kernels in the inner fluid of the embryo 
sac increase in size and number; most of them lie now against 
the wall of the embryo sac; . . . they unite with the cells which 
fill up the space of the embryo sac. The lower part of the nucellus 
is pressed continually outward by the growing endosperm as the 
seed ripens.”’ 
At first it was impossible to kill and fix the early stages of the 
embryo. This difficulty was due to the fact that a suitable killing 
and fixing agent which would not cause great shrinkage of the 
protoplasm in these particular stages was not known. Therefore 
free hand sections or sections cut on a freezing microtome were used. 
The working out of the anatomical details of the developing embryo 
becomes possible with the use of a two per cent. acetic acid in 
water solution as a killing and fixing agent. 
After fertilization the odspore continues to occupy the same 
position as the odsphere. It enlarges (Fic. 7) and soon divides 
Soon after the first division of the 
by a transverse wall (FIG. 9). 
h the nucellus 
odspore, the two-celled proembryo is in contact wit 
at the micropylar end of the embryo sac, and a little later is 
firmly attached at the same point. The basal cell of the pro- 
embryo develops into a suspensor, while the free terminal cell 
gives rise to the embryo proper (Fic. 10). The second cell 
division of the proembryo occurs in the basal cell, resulting in the 
