372 STEVENS. DISCOID GEMMAE IN LEAFY HEPATICS 
4, Aand B). The marginal cells, however, rarely divide by walls 
parallel to the surface and the basal cells never take part in this 
division. In this respect R. complanata apparently differs markedly 
from other members of its group. For in all the other leafy 
Jungermanniales thus far observed, which bear thalloid gemmae, 
the gemmae are but one cell thick throughout (Evans, 298). 
In the mode of separation of the gemmae, also, Radula com- 
planata differs from many other leafy Jungermanniales. For while 
the separation is schizolytic, the splitting takes place in the wall 
between the basal cells and the cells of the leaf. The two-celled 
FIGURE 4. Radula complanata. A and B. Mature gemmae in optical rec- 
tion. C. Surface view of mature gemma. X 300. 
stalk is thus retained asa part of the mature gemma when it falls 
from the plant. This is very different from the condition found 
in Cololejeunea, where the separation takes place between the 
gemma and the stalk cell. A similar difference has been noted by 
Evans (277, 284, f. 4, 9) in the separation of the gemmae in Mets- 
geria. In M. crassipilis, for example, the gemmae are set free 
by a splitting of the wall between the gemma and the cell cut off 
by the original horizontal wall, while in M. furcata separation 
takes place by the basal cells splitting away from the adjacent 
thallus cells. 
In no case was a mature gemma observed which still retained 
an apical cell. This is contrary to the statement of Cavers (159) 
that the mature gemma “‘shows on its distal margin a large apical 
cell, triangular in surface view.”’ 
