Bliss. — A Contribution to the Life-history of Viola . 159 
of the sac is an irregular vacuole, two-thirds as long as the entire 
embryo-sac. 
The embryo-sac continues to lengthen and broaden, the nuclei at either 
pole divide simultaneously, and the four-nucleate stage is established. At 
this stage, the embryo-sac is twice as long as at the two-nucleate stage, but 
the comparative length and breadth are the same. The third division soon 
follows, and gives rise to the typical eight-nucleate embryo-sac of Angio- 
sperms. Immediately after this division, the three cells which are to form 
the egg apparatus increase rapidly in size, surround themselves with a 
delicate cytoplasmic membrane, and begin to assume their characteristic 
shape. The egg extends from the apex of the sac about one-third its 
length. The protoplasm is condensed in the basal portion of the egg, 
and in it lies the nucleus, close to the basal line. Just above the dense 
cytoplasm is a large vacuole, which occupies fully two-thirds of the entire 
egg. The synergids are not quite as long as the egg- cell. They are pointed 
at the apex and broadly oval at the base. The upper portion of each is 
filled with dense cytoplasm, while the lower one-third of the cell is occupied 
by a large vacuole, characteristic of synergids in the majority of Angio- 
sperms investigated. The nucleus generally lies in the middle of the cell, 
surrounded by dense cytoplasm, but quite close to the vacuole (Fig. 15). 
While the egg apparatus is being formed in the micropylar end, various 
changes are taking place at the antipodal end of the sac. The antipodal 
polar may be distinguished from the other antipodal cells at an early stage 
by its greater size and larger nucleus. The usual number of antipodals in 
Viola is three. Their development and arrangement is varied. In some 
preparations the antipodals appear as definite cells with distinct limiting 
membranes, in others the antipodal nuclei lie naked in the general cytoplasm 
at the base of the sac. The antipodal cells are generally much smaller than 
those at the micropylar end, but their nuclei are large and, almost without 
exception, each contains a single nucleolus. These cells may be arranged 
in a row, side by side, or in a quadrant. As a rule the antipodals are not 
conspicuous, and in many cases when the embryo- sac is fully mature, the 
antipodals have already disappeared or are present merely as disintegrated 
masses at the basal end of the sac. In only one instance observed was there 
any suggestion of the haustorial development of the antipodals as described 
for the Rubiaceae (Lloyd, 6), Aster (Opperman, 8), and other genera 
(Fig. 17). 
Soon after the egg apparatus has been established, the polar nuclei 
move towards each other. The antipodal polar moves more rapidly than the 
micropylar polar, consequently fusion is often completed just beneath the 
egg. At first nucleus only fuses with nucleus, and for some time the 
nucleoli remain distinct. Finally, however, the nucleoli fuse, and the result 
is a large endosperm nucleus twice the size of either polar nucleus. The 
