102 Hill—The Structure and Development of 
distinguish the primary segment-walls, but in later stages 
this becomes increasingly difficult. 
By subsequent growth in length the spherical embryo is 
converted into one of a more oval shape, as illustrated in 
Fig. 42. From this figure it may be seen that the basal cell 
is still attached to the embryo, and that there is a narrow 
chain of suspensor-cells. 
The basal cell becomes detached from the embryo, but 
may be recognized for some time, until the embryo is well 
on its way to maturity. The stem-apex just arising is shown 
in Fig. 42, and from this it will be seen that, as in so many 
other Monocotyledons, the stem-apex arises laterally. 
The mature embryo is straight, and not curved over, as 
is found in Alisma Plantago , and a second leaf is frequently 
differentiated while still in the seed. 
The formation of the Endosperm. 
The first division of the definitive nucleus was observed 
in an embryo-sac in which the oosphere had been fertilized 
(Fig. 33); the two nuclei thus formed were found to be 
in a state of division when the embryo was a two-celled 
structure (Fig. 34). 
The endosperm-nuclei formed are very distinct, each having 
a conspicuous and somewhat large nucleolus. These nuclei 
are not very numerous, considering the size of the embryo-sac, 
and they arrange themselves in the protoplasm which lines 
its walls. In no case were cell-walls observed between them, 
Triglochin thus differing from the endosperm of Sparganium 
and Lysichitoii) and resembling that of Lilaea subulata. 
