172 BOTANICAL GAZETTE [SEPTEMBER 
In the investigation of the typical germinations of Phycomyces, 
it has been shown that the determination of sex does not occur in 
the zygote, but that an interval in the form of a germ tube is inter- 
polated between the zygote and the germ sporangium where the 
segregation of sex finally occurs. The essential difference between 
Phycomyces and Marchantia lies in the fact that in the former the 
interval is a single-celled multinucleate structure arising from a 
multinucleate zygospore, while in the latter the interval is made up of 
many uninucleate cells arising from a uninucleate oospore. In Mar- 
chantia-the segregation of sex undoubtedly takes place at some point 
in the maturation of the sporangium. If the archesporium and the 
spore mother cells prove capable of germinating, and it be possible 
in the thalli which result to recognize the presence of both sexes 
when the plants are homothallic, one may be in a position to deter- 
mine the exact point where the segregation of sex occurs and to 
discover what relation if any the segregation may have to the reduc- 
tion division or to other nuclear phenomena. 
The predominance of organs of a single sex on the prothallus of 
the ferns due to conditions of growth and the similar phenomenon 
in the sporophyte of Selaginella may lead to the non-appearance of 
the other sex. Such a suppression of sex, however, is not to YF 
confused with sex determination. By cultivating fern prothalli 
under unfavorable conditions of nutriment, PRANTL (15) Was able 
to confine the production of sexual organs to antheridia. The 
archegonia demand a prothallus furnished with meristematic tissue, 
and consequently on a poorly nourished prothallus which has de- 
veloped no meristem only antheridia can be formed. If prothalli 
which are producing exclusively antheridia be removed from a culture 
medium containing no available nitrogen, to a medium in which 
available nitrogen is present in sufficient amount, meristematic 
tissue is developed upon which archegonia are formed. KLEBS 
(12), moreover, has shown that by reducing the amount of light to 
which they are exposed prothalli may be brought to a prolonged 
vegetative growth, and thus the formation of both antheridia and 
archegonia may be suppressed. Professor KLEBS has informe 
the writer that when the amount of light is increased to a certal” 
extent, antheridia alone are produced from these sterile prothalli, 
