18 
H. MARSHALL WARD. 
a third division across the embryo-sac mother-cell, and not 
as the first division of the contents of the macrospore 
(embryo-sac). In other words, we have here a division wall 
still weaker than the two preceding, and the vacuole 
is its expression. If this be so, it is possible that the 
embryo-sac mother-cell is really the mother-cell of four 
spores, two of which (the cap-cells) yield up their contents 
to their more vigorous neighbours — to the other two, which 
never completely separate, but form an embryo-sac,” and 
its contained apparatus. 
This suggestion does not exclude the view that the eight 
nuclei derived from that of ihe embryo-sac mother-cell are 
cells of rudimentary prothalli, but explains them as belong- 
ing to prothallial structures instead of one ; the one pro- 
duces a rudimentary archegonium (the egg-cell with its 
synergidse may perhaps be an oosphere and two neck-cells), 
and one vegetative cell ; the lower spore produces four vege- 
tative cells. How to explain the subsequent fusion of one of 
these from each group is not easy, unless some advantage 
accrues to the large embryo-sac, by having a nucleus ren- 
dered vigorous by material from two slightly different 
sources. This is, however, too hypothetical to enlarge upon 
here, and perhaps we are yet far from possessing the facts 
necessary for an explanation of this remarkable process. 
