366 STEVENS: DISCOID GEMMAE IN LEAFY HEPATICS 
in March, and at Lentz, Switzerland in September, being used for 
comparison. All the Radula material used was collected by Pro- 
fessor A. W. Evans. 
But little has been written concerning the gemmae of the leafy 
Jungermanniales. In the tropical genus Cyclolejeunea, however, 
the gemmae have been described by Evans in four species. In 
Cololejeunea the development and structure of the gemmae have 
been described by Goebel in the Javan C. Goebelii (Gottsche) 
Schiffn. and by Cavers in the European C. calcarea (Lib.) Schiffn. 
For Radula the development of the gemmae has also been briefly 
treated by Goebel in two Javan species, R. Hedingeri Goeb. and 
R. tjibodensis Goeb., and by Cavers in R. complanata. 
COLOLEJEUNEA BIDDLECOMIAE. 
The gemmae in Cololejeunea Biddlecomiae are borne on the 
surface of the leaves, most frequently on the lower surface of the 
lobes, occasionally on the upper surface and never, at least in the 
material examined, on the lobules. Usually only a few, not more 
than five or six, are borne on a single leaf. Gemmae appear to 
be of rather general occurrence in this species, though only a com- 
paratively small proportion of the plants in any individual mat 
are gemmiparous and plants bearing a considerable number of 
gemmae are found closely associated with plants having none. 
Gemmae are found more abundantly on sterile plants, but the 
presence of sexual organs by no means prevents the formation of 
gemmae. In fact they are found occasionally on the bracts, but 
never, so far as could be determined, on the perianths. 
In the formation of a gemma a leaf cell first projects beyond 
the surface of the leaf and the projecting portion is cut off by a wall 
parallel to the leaf surface. The outer cell, which is nearly cir- 
cular in outline, becomes the mother-cell of the gemma, while 
the inner one may be regarded as a stalk. The gemma mother- 
cell then undergoes a series of regular divisions by walls perpen- 
dicular to the surface of the leaf. The first wall divides it into two 
approximately equal parts (FIG. 1, A) and each of the semicir- 
cular cells then divides by a wall perpendicular to the first, so that 
the gemma in the four-celled stage consists at first of approxi- 
mately equal quadrants (FIG. 1, B). 
