Farmer. — On Isoetes lacustris , L. 59 
that Pfeffer was in error in regarding the ‘ Endosperm ’ of 
Selaginella as representing anything more than the vegetative 
or specially nutritive portion of the prothallium : the differences 
in the character of the cell-division in the two regions arising 
from the fundamental difference between the respective proto- 
plasms (in the widest sense of the word) which so modify the 
manner of cell-formation as to suit the ultimate requirements 
of each. 
I believe these conclusions may serve further to throw light 
on the question of the significance of the changes which occur 
in the embryo -sac of Angiosperms up to the period when the 
oosphere is ready for fertilization. Just as in Selaginella and 
Isoetes the first divisions of the spore separate the reproductive 
from the vegetative protoplasm, each of which thenceforth de- 
velops on different lines, so also the first division of the nucleus 
of the embryo-sac produces two daughter-nuclei, whose further 
products are perfectly dissimilar, resulting finally in the pro- 
duction of the ‘ egg-apparatus ’ at the one end, and the anti- 
podal cells at the other, with the definitive nucleus half-way. 
The antipodal cells do not, I believe, represent the whole 
prothallium, as they are usually considered to do, but only 
the reduced vegetative portion of it. And it would seem that 
the reduction has progressed so far that the original vegetative 
part is unable to, or at least does not, fulfil the needs of the 
growing embryo as regards nutriment, and hence the coales- 
cence of the two nuclei, one from the reproductive (micropylar) 
and one from the vegetative (antipodal) part of the pro- 
thallium. 
The definitive nucleus, formed in this manner, may probably 
be regarded as the result of a coalescence of nuclei analogous 
to that which obtains in actual fertilization, but with this 
difference, that in this case it is not an oosphere, but probably 
the second polar body , which descends from the generative 
apparatus and fuses with a vegetative nucleus which is derived 
from the opposite end of the spore. The union does not confer 
great power on the resultant nucleus : merely that of forming, 
under certain conditions, a number of similar cells — the endo- 
