Campbell.—The Embryo-sac of Pandanus. 781 
istics different from those in the ordinary embryo-sac. The nuclei are about 
half the size of the primary micropylar nuclei, and the nucleolus is relatively 
larger and more conspicuous. The second micropylar nucleus presumably 
gives rise to the nucleus of the egg and a free nucleus, the upper polar 
nucleus (/. nf This upper polar nucleus later moves towards the base of 
the sac and fuses with the lower polar nuclei to form the primary endo¬ 
sperm nucleus. 
The cytoplasm of the egg-cell, which is not always very clearly 
differentiated, is less dense than that of the synergidae, and the nucleus, 
sometimes at least (see Fig. 22, c), is smaller, with a less conspicuous 
nucleolus. 
The polar nucleus is at first in close contact with the egg, and in size 
and structure resembles its sister nucleus. As it moves towards the lower 
part of the embryo-sac it becomes very much larger, and at the time it 
fuses with the polar nuclei from the antipodal end it is impossible to dis¬ 
tinguish it from them. 
The Antipodal Cells. 
The exact number of antipodal cells is not easy to determine, as 
sometimes the nuclei of the adjacent nuclear tissue become enlarged and 
strongly resemble the nuclei of the antipodal cells, with the outermost of 
which they may readily be confused. Moreover, there is undoubtedly 
much variation in the number of antipodal cells. In several cases thirty-two 
of these could be counted, while in others there were as many as sixty-four, 
and possibly the number may be even greater than this. In some of the 
preparations a number of the antipodal nuclei were in process of division, 
but no rule could be discovered governing the time of division. It is 
probable that the number of antipodal cells present at the time fertilization 
takes place depends, at least in part, upon the number of free nuclei in the 
chalazal region at the time cell-formation begins. So far as could be 
determined the number of these free nuclei may range from eight to 
fourteen, and it seems likely, although this could not be proved, that the 
next division in these nuclei is accompanied by the formation of cell-walls. 
The antipodal cells (Figs. 22-4) are of very irregular form and contain 
a good deal of granular cytoplasm which is more or less vacuolated, 
especially in the upper cells. These cells in the earlier stages are strongly 
turgescent, and the upper ones project into the cavity of the embryo-sac. 
In the later stages these upper cells appear more or less flattened or even 
collapsed (Fig. 125), but how far this is the normal appearance, and 
how far it is due to shrinkage in the preparation of material, is impossible 
to say. 
From one or more of the upper cells the large nuclei are discharged 
into the cavity of the embryo-sac and constitute the lower polar nucleus 
3 F 
