170 BOTANICAL GAZETTE [SEPTEMBER 
The “dioecious” phanerogams, represented by the heterophytic 
form Populus, follow closely the Mucor Mucedo type. They differ 
from Mucor Mucedo in that the sexual differentiation has reached 
a morphological expression, and the sex of the thalli, spores, and 
sporangia is at once distinguishable. In general the male and female 
sporophytes are alike in appearance, but in the sporophytes of some 
forms the sexes are easily distinguished. Perhaps the best known 
example among the common trees is the Lombardy poplar (Populus 
pyramidalis), which in male specimens has been widely cultivated 
for the sake of its pyramidal form. The female trees have a spread- 
ing habit of growth and are seldom to be found in cultivation. 
In the diagram three squares are left blank. In the flowering 
plants heterothallism has become fixed and no forms of the Sporo- 
dinia type exist. There is no reason apparent why heterophytic 
forms should not occur among the heterothallic pteridophytes. The 
fact remains that all the existing heterothallic species are homophytc. 
The blank squares in the phanerogams and pteridophytes must there- 
fore remain unfilled, Little is known about the sexual differentiation 
in the bryophytes, and it must rest with future research, therefore, 
to determine whether or not they possess heterophytic representatives 
in the heterothallic group. 
In light of the conditions found in the Mucorineae, the hetero- 
thallic bryophytes, as already pointed out by the writer (/. ¢., P- 25), 
offer a most interesting field for investigation. Accordingly nee 
tion was directed to the heterothallic form Marchantia polymorpha, 
which, according to the unpublished observations of NOLL as reporte 
by ScHULTZE (17), retains the unisexual character of the individual 
thalli when propagated vegetatively by gemmae. 
During the last November, Marchantia was found in fruit and 
sowings were made from individual sporangia, and the young plants 
resulting from their germination were isolated and transplanted 1 
such a manner that at fructification it would be possible to determine 
the sex of the individual spores from which they were derived. While 
the present paper was largely in manuscript, the writer learned of 
unpublished observations made by Nott on this same species. Pro- 
fessor Nott, to whom the writer is greatly indebted for the inform 
tion communicated, has cultivated Marchantia by means of gemmat 
