STUDIES IX THE DEVELOPMENT OF THE PIPERACEAE 729 
and the segregation of sexes, or suppression of one sex must there- 
fore occur between the fusion of gametes and the germination of 
the zygospore, and must result in the suppression now of the 
male, now of the female tendency, in the mycelium coming from 
the zygospore. 
Among the Bryophytes, it seems clear from the work of Blakes- 
lee on Marchantia ('06), the Marchals on mosses ('06, '07), and 
of Strasburger ('09) on Sphaerocarpus, that the segregation of 
sexes takes place at spore-formation, probably during meiosis. 
In homosporous ferns each sporophyte is usually clearly her- 
maphrodite, each spore also, and the prothallus coming from it, 
is usually bisexual, for though the male organs onl}^ may be devel- 
oped at first, the female organs are usualh' formed later, on all 
well-nourished prothalli. Segregation in this case, if it can be 
called such, evidently takes place during the later development 
of the gametophyte. 
The heterosporous ferns and Selagiiiella give the first clear 
indication, after that noted in Mucor mucedo and possibly Fucus, 
of the segregation of the sexes at a point in the development of 
the sporophyte other than sporogenesis. In MarsiHa, e.g., the 
gametophyte is never hermaphrodite, but distinctly male or 
female. The sporophyte, on the contrary, is hermaphrodite and 
retains this condition, so far as can be seen, up to the time of the 
separation of the three marginal cells of the seventh grade, in 
the sporocarp, which give rise to all the thirty or forty micro- 
sporangia and megasporangia of each sporus (Johnson, '98, figs. 
34, 38). Shattuck ('10, p. 23) states that all the sporangia of 
Marsilia have the same development up to the time that spore- 
mother-cells are formed, after which the microspores and mega- 
spores are markedly different in character. He states further 
that changing the conditions surrounding the plant, at the proper 
time of development, may cause the young spores in certain of 
the microsporangia to become enlarged, and to assume somewhat 
the type of spore wall of the normal megaspore. He has not, 
however, yet been able to germinate these enlarged spores, and 
has therefore failed to demonstrate conclusively that these have 
