1906] BLAKESLEE—DIFFERENTIATION OF SEX 171 
for over thirty generations of both male and female strains, without 
having been able to change the sexual character of the thalli by sub- 
jecting them to varying conditions of growth. The form is therefore 
strictly heterothallic. Moreover, in a single instance a sporangium 
was made to discharge its spores on a pot of earth, and male and 
female fructifications were obtained from the mixed growth of thalli 
resulting from their germination. Marchantia is therefore homo- 
phytic, and it now becomes possible to fill out in the diagram one of 
the two squares which in the bryophytes had been left blank pending 
the fructification of the young thalli which the writer had obtained 
from isolated spore germinations.? 
In Phycomyces, with which Marchantia is to be compared, there 
seems to be no definite relation between the number of male to female 
spores formed in a germ sporangium, and it may even happen that 
all the spores are of the same sex. Moreover, it is not infrequently 
the case that in a small per cent. of the spores in a germ sporangium 
the segregation into male and female has not been completed. 
These bisexual spores produce homothallic mycelia. Cultures from 
individual spores will be necessary to determine for Marchantia 
the proportion of male to female spores in a single sporangium, and 
to ascertain if, in addition to the normally unisexual spores, bisexual 
spores are ever formed, as is the case in Phycomyces. 
The bisexual germ tube of Phycomyces may be cut and forced to 
branch out to a homothallic mycelium. The observations of Nott 
and of the writer have shown Marchantia to be homophytic. Its 
sporophyte as a whole, therefore, must be bisexual, and every cell 
formed before-the determination of the sex of the spores, if brought 
to develop into a new plant, should theoretically produce homothallic 
individuals. PRrincsHErm (16), STAHL (18), and CoRRENS (10), 
among others, have obtained protonemata from the sporophytes of 
mosses. -No one, however, seems to have succeeded in obtaining 
Tegeneration from the sporophyte of liverworts. The writer has 
experimented with mature sporophytes of Fegatella and with sporo- 
phytes of Marchantia of various ages, but has been unable to secure 
any growth from them. 
? While the present paper is in press, 12 thalli have so far produced seater 
out of a total of rx '3 which were obtained from as many spo res from a single spo 
gium. Of these nine are male and three are female. 
