APRIL 5, 1901.] 
of the relation of the special mother cells 
to the subsequent tetrads in the embryo- 
sac, the figure of the tetrad suggesting that 
each nucleus corresponds to a spore or pol- 
len grain. 
5. A fifth view, and one which was 
also influenced to some extent by Warm- 
ing, was proposed by Marshall-Ward (Jour. 
Mier. Soc., 20, 1880; also, Jour. Linn. Soc., 
7, 1880). According to this view the em- 
bryo-sac consists of two prothallia, de- 
rived from two spores, the ege apparatus 
representing one, and the antipodals repre- 
senting the second. The upper one consists 
of one vegetative cell (the upper polar nu- 
cleus) and the rudimentary archegonium, 
the two synergids being suggested as neck 
cells. The origin of the embryo-sac ac- 
cording to this view, wasas follows: The 
primary mother cell of the embryo-sac, 
either a subepidermal cell, or the lower de- 
rivative of this, when a tapetum is formed, 
divides once and forms two cells. The 
lower one divides again, thus forming three 
cells in the axile row, separated by cell 
walls. ‘These three cells correspond to the 
special mother cells which Warming believed 
to be homologous with the pollen mother 
cells. The lower cell now develops the em- 
bryo-sac. Its nucleus divides in the same 
direction as the division walls arising in 
the formation of the three cells of the axile 
row. ‘These two nuclei at opposite poles 
of the young embryo-sac he believed rep- 
resent cells in the axile row, thus mak- 
ing four cells in all. The two lower cells 
are not separated by cell walls, due, he 
believes, to the extraordinary rapidity of 
growth from this time onward. Each of 
these two lower cells, represented by the 
two-nucleated stage of the embryo-sac, he 
interpreted as a spore, one to give rise to 
the upper prothallium, and the other to the 
lower prothallium of the embryo-sac. It 
is possible to draw the inference that he 
regards the primary mother cell of the em- 
SCIENCE. 
533 
bryo-sac as a mother cell of four spores, 
since the axile row, as he interprets it, con- 
sists of four cells. The two lower ones he 
distinctly interprets as spores. The pri- 
mary mother cell could not, however, be a 
cell homologous with the mother cell of 
spores according to this interpretation, since 
three successive divisions occur before these 
two spores are developed which are to form 
the embryo-sac; while the tetrad of real 
spores is developed by two successive di- 
visions. 
6. A sixth theory of the homology of the 
embryo-sac was proposed by Mann. (The 
embryo-sac of Myosurus minimus L., Trans. & 
Proc. Bot. Soc., Edinburgh, 29, 35; 1892. 
The embryo-sac of angiosperms is a sporo- 
cyte and not a macrospore, Ann. Rep. B. 
A. A. S., 782, 1892.) He made an attempt 
to draw a direct homology between the 
embryo-sac and the pollen mother cell in 
origin, and also in the number of nuclei 
developed as a result of the division of the 
mother cell or sporocyte. For him each 
cell of the axile row is a sporocyte, and 
homologous with the pollen mother cell. 
Since from the pollen mother cell the four 
spores (pollen grains) are formed, and each 
pollen grain at maturity contains two nu- 
clei, making eight in all, he traced a direct 
and parallel homology in the origin of the 
eight nuclei of the embryo-sac. The four- 
celled stage of the embryo-sac represents 
the four spores which are homologous with 
the four pollen grains. Each nucleus now 
divides again into a vegetative nucleus and 
a sexual nucleus, which correspond to the 
vegetative nucleus and generative nucleus 
of each pollen grain. In thus tracing the 
homology of the eight nuclei of the embryo- 
sac with the eight nuclei in the four pollen 
grains, Mann overlooks the fact that prior 
to fertilization, when the embryo-sac is still 
in the eight-nucleated stage, the generative 
cell in the pollen tube has divided again, or 
in some cases it divides by the time the pollen is 
