74 _ BOTANICAL GAZETTE [JULY 
the diploid sporophyte. In heterosporous plants there is no sex differentia- 
tion except that which leads to the formation of microspores and megaspores, 
for from a microspore mother cell come four spores which produce only male 
products, and from a megaspore mother cell come four spores which produce 
only female products. If all sporophytes were bisexual, the problem would be 
comparatively simple, but there are sporophytes which produce only micro- 
sporangia or only megasporangia, and these dioecious seed plants, although 
their number is comparatively small, have been used extensively in the study 
of sex problems. 
A large amount of experimental work is recorded, the principal forms 
used being Mercurialis annua, Melandrium rubrum, and Elodea canadensis. 
In Mercurialis annua ovulate plants sometimes bear occasional staminate 
flowers, and similarly, Seshices plants sometimes bear occasional ovulate 
flowers. STRASBURGER had already found that the flowers of an ovulate 
S 
flowers on a staminate plant, when pollinated from the same plant, bear seeds 
which produce only staminate plants. Some plants have ovulate flowers with 
staminate flowers growing up through them in a sort of proliferation. Pol- 
lination of such ovulate flowers with pollen of the proliferating flowers gives 
rise to seeds which produce both ovulate and staminate plants. The con- 
clusion is that in the scattered staminate flowers the male tendency has become 
weakened, and that in the scattered ovulate flowers, the female tendency has 
become weakene 
In the Rinectons Melandrium rubrum, pollination was effected by pollinat- 
ing with thin transverse sections of still unopened anthers. It was hoped that 
grains with the stronger and with the weaker male tendencies. In all, 1475 
seeds were secured, and from these there were obtained 1124 seedlings, 1035 
of which reached the flowering stage. Of these 376 were staminate and 659 
ovulate, the ovulate being strongly dominant. * 
The work on Elodea canadensis is interesting, but is still in an unfinished 
condition. Although ovulate plants have long been abundant in Europe, 
staminate plants are not available. Staminate plants and seeds were secured 
from Wolf Lake, near Chicago, and hundreds of stigmas were pollinated, each 
with a single pollen tetrad. Fertilization has taken place, but seeds are not 
yet ripe. If each ovary should produce four seeds, two of which should pro- 
duce staminate plants and two ovulate plants, there would be some definite 
dat 
The general conclusion from the data, only a small part of which has been 
indicated here, is that all eggs are female and all pollen male, but that some 
pollen has a strong and some a weak male tendency. Pollen with a strong male 
tendency overcomes the female tendency of the egg, while pollen with the weak 
male tendency is overcome by the stronger female tendency of the egg. The 
Se 
