ENDOSPERM 17 
median lateral region and one in the anterior portion of the sides. 
All these branches produce short spurs and anastomose rather 
freely near their distal extremities. The sixth strand, which 
must be considered the extension of- the main axis, passes into 
the plumule and scale leaf. 
The diagram and description given are intended to cover 
only the more constant features. The differentiation of the parts 
depends upon the development of the embryo as a whole. In 
some seeds whose development was cut short by an early drought, 
but which, none the less, were viable and produced vigorous 
seedlings, the embryos showed scarcely a trace of vascular strands. 
In others with long growth period, the primary xylem elements 
were evident before germination. 
THE ENDOSPERM 
At the time of the entrance of the pollen tube the embryo-sac 
contains a normal egg apparatus, three inactive, shrunken antip- 
odals and an endosperm nucleus. This endosperm nucleus, 
found usually near the chalazal end but sometimes near the middle 
or even in the micropylar end of the sac, is the most conspicuous 
nucleus in the cavity. A little before the fusion of the sperm 
and egg nuclei, the endosperm nucleus divides. Whether or not 
there is a fusion of one male nucleus with the endosperm nucleus 
can not be stated positively. Gow (13) states that a second male 
nucleus enters the embryo-sac and approaches the endosperm 
nucleus; but he did not observe any fusion or even contact of the 
two. The writer has not seen any direct proof of such a fusion; 
but its occurrence is suggested by the fact that division of the 
endosperm nucleus has been found only at a time shortly after 
the entrance of the pollen tube into the embryo-sac. This relation 
is further indicated by the failure of the endosperm nucleus to 
divide in embryo-sacs untouched by pollen tubes, a fact abun- 
dantly proved by the careful examination of numerous sterile 
ovules beside those developing into normal seeds as well as those 
from spikes protected from possible pollination. The finding of 
but six examples of the division of the endosperm nuclei in one 
bunch of 150 ovules showing stages from mere entrance of the 
pollen tube up to the formation of the first walls between the free 
