O’ NEAL: EMBRYO SAC DEVELOPMENT IN OENOTHERA 143 
seems so unlikely as to warrant comment, even though out of 
the scope of this paper. According to this theory, the pollen 
tubes act as antigens and stimulate the formation of specific 
antibodies by the cells of the pistil. The outstanding objections 
to this belief are: (1) that there isnocomplete circulation in plants 
as in animals, so that but comparatively few cells could be 
stimulated, and (2) that the time between pollination and fertiliza- 
tion is too short for the development of anti-substances in suffi- 
cient quantities to produce such a striking effect, even if the 
circulation in plants were in all ways the same as in the higher 
animals. 
Ishikawa (17) found that fertilization was double in Qe. 
pycnocarpa and Oe. nutans and Modilewski (21) reported it as 
probably double in Oe. biennis. The writer has been unable 
to confirm this finding in Oe. rubrinervis and has the feeling that 
it does not occur in this plant. The chromosomes were not 
counted in the endosperm and the whole point requires further 
investigation. It is needless to state that the Oenotherae do not 
furnish ideal material for fertilization studies. 
SUMMARY 
1. The ovules of Oenothera rubrinervis arise in the usual 
fashion from a slight swelling that appears upon the wall of 
the ovary. 
2. Early in the development of the ovule an archesporial 
cell is differentiated that soon divides into an outer tapetal 
initial and an inner primary sporogenous cell. 
3. The tapetum initial gives rise to a tapetal row of about a 
dozen cells, and the primary sporogenous cell develops into the 
usual potential megaspore tetrad. 
4. The cell of the tetrad nearest the micropyle usually 
becomes the functional megaspore, although in some cases the 
one at the opposite end of the row may develop. 
5. Early in the development of the megaspore, a large 
central vacuole appears which persists until after the embryo 
sac development is completed. 
6. Upon germination the nucleus of the megaspore divides 
but twice, so that the mature embryo sac contains but four 
nuclei instead of the usual eight. 
