1904 | WYLIE: -ELODEA CANADENSIS 5 
being six or eight times larger than the micropylar one. In the 
division of these daughter-cells the spindles show a corresponding 
difference in size and vary in direction, especially in the outer 
cell, in which it may lie at right angles to the longer axis of the 
ovule (figs. 26, 27). Four megaspores are usually formed, which 
are separated by walls. In one instance it was observed that the 
two central cells of the row of four had each divided again, 
resulting in six megaspores (jig. 28). This case was made very 
clear as the megaspore at either end of the row had enlarged, 
thus lessening the possibility of confusing sterile cells with 
megaspores. This particular row is of interest also in showing a 
struggle for dominance between the innermost and outermost 
cells. In all other cases noted there were but four megaspores, 
and the innermost one seems regularly to be the successful one 
(fig. 29). 
With the division of the megaspore there is introduced a 
change in the form of the embryo sac, which, though often seen in 
later development, is seldom introduced at so early astage. The 
' upper one-third of the embryo sac begins to enlarge, and by the 
time this first division is completed has a diameter nearly twice 
that of the cylindrical part beneath (fig. 30). As development 
proceeds this differentiation becomes more marked. The outer 
part, in which all the growth takes place, continues to enlarge, 
being at first spherical, then oblong, and finally assuming the 
usual embryo sac form. The inner part persists with dimensions 
unchanged or somewhat diminished by encroachments of the 
main body of the embryo sac (jigs. 31-36). While such a 
pouch-like antipodal end is not uncommon, the emphasis laid on 
its early development in this instance might suggest its being a 
rudiment of a once prominent nutritive device, but it probably 
functions-now in no important way. 
At the two-celled stage one nucleus passes to each end of 
the sac (fig. 30). The divisions giving rise to the antipodal 
group occur deep within the pouch (figs. 37,32). The spindles 
seen here are much smaller than those of the micropylar end, and 
the resultant nuclei of the two groups show a proportional differ- 
ence in size (fig. 32). 
