368 STEVENS: DISCOID GEMMAE IN LEAFY HEPATICS 
in the material containing precisely the same number of cells, yet 
having a diameter of 0.055 mm. or more. The cells of the gemma 
meanwhile increase proportionately in size, that is, from about 7 u 
to about 12 uw in average diameter or to slightly less than the aver- 
age diameter of the cells of the lobe. 
A mature gemma is typically a flat disc consisting of a single 
layer of cells and showing no indication of dorsi-ventral differen- 
tiation. It is composed of symmetrical halves, each consisting 
of eleven or twelve cells... In each half eight of these cells come 
from the apical cell and its three segments and three or four come 
from the basal cell (FIG. 1, F). The gemma is regular in outline, 
without marginal hairs or other projecting cells, and there is no 
indication of rhizoids or other organs of attachment such as de- 
scribed by Goebel in the epiphyllous C. Goebelit. The one-celled 
stalk is attached to the gemma along the median line in the basal 
region (FIG. 1, F and G). The separation of the gemma takes 
place as in other Lejeuneae by the splitting of the cell wall between 
the stalk cell and the gemma. 
The above description agrees closely with Goebel’s account (50, 
f. 55) of the development of the gemma in Cololejeunea Goebelii, 
except that he describes the first anticlinal wall as dividing the 
semicircular cell into unequal portions. This condition in C. 
Biddlecomiae, at least, seems to be secondary, due to the more 
rapid growth of the cells which are to function as apical cells. 
This appears from the fact that the condition of equal quadrants 
(FIG. 1, B) is of frequent occurrence in the four-celled stages 
observed. 
The development of the gemmae in Cololejeunea Biddlecomiae, 
as traced by the writer, differs in several respects from that figured 
by Cavers (160, f. 8) in the closely related C. calcarea. Cavers 
figures the cell divisions as taking place by cell walls parallel to 
and at right angles to the median line, without reference to an 
apical cell, and implies that the mature gemmae differ from those 
of C. Goebelit in not having an apical cell. He states also that 
the stalk cell is inserted at the center of the gemma. In order to 
determine whether C. calcarea teally differs from other members 
of the genus in these respects, material from Pottenstein in Upper 
Franconia, Germany, collected by Arnold (Hep. Europ. 2836) 
