1900] DEVELOPMENT OF THE EMBRYO-SAC 35 
times, until the steps became so clear as to leave no doubt 
in the mind of the writer that the description as given above is 
correct. 
To summarize briefly: the mature embryo-sac consists of an 
egg and two evanescent synergids, each without a cell-wall of 
its own, but all contained. within a pouchlike cavity separated 
from the general cavity by a delicate wall. One synergid usu- 
ally disappears before fertilization. Next below is a large cav- 
ity containing the endosperm nucleus, and later the endosperm, 
derived without fusion from the lower polar nucleus. At the 
base are the four antipodal cells, three of which are very small 
and chromatic, and are descendants of the same nucleus, while 
one is very large and together with the polar nucleus is derived 
from another parent. The antipodals are separated from the 
main cavity by a membrane formed at the time of separation of 
the polar nucleus and the antipodal cell. The endosperm even 
after fertilization never becomes more than a parietal layer 
(fig. 24). 
The investigation of plants of the same and nearly related 
orders has shown that the occurrence of the large antipodal 
nucleus is not a peculiarity of Potamogeton alone, but is charac- 
teristic of a whole group of Monocotyledons. Schaffner? found — 
that in Sagittaria the development was normal up to the forma- 
tion of the two synergids, egg, and three minute antipodal cells. 
He then found that the two polar nuclei fused in the ordinary 
way, after which the definitive nucleus underwent division. This 
division was always followed by a transverse wall enclosing one 
of the daughter nuclei in a chamber at the base; and this was 
the one which became so large at a later period. Sometimes 
several were found, thus showing that the large nucleus had 
divided at least once or twice. From the other daughter nucleus 
Was produced the endosperm. The structure in question was 
therefore thought to be an endosperm nucleus, rather than an 
antipodal cell as in Potamogeton. 
7 SCHAFFNER : Contribution to the life history of Sagittaria variabilis. Bot. Gaz. 
23: 252. 1897. 
