206 _ Evans: HEPATICAE OF PUERTO RICO 
other cells and functions asa stalk. The gemma is attached to 
the stalk-cell by two basal cells which can usually be distinguished 
by their greater length. The separation of the gemmae is by a 
schizolytic process, which leaves intact both the stalk-cell and the 
two basal cells of the gemma. The development, structure and 
germination of the gemmae differs somewhat in the various spe- 
cies and will be described in considerable detail. 
In Cyclolejeunea accedens, which will be taken up first, the 
gemmae arise normally from the antical margin of an unmodified 
leaf. One of the pointed marginal cells bulges slightly beyond 
its neighbors and becomes enlarged at its extremity. The en- 
larged portion is then cut off by a wall and forms the mother-cell 
of the future gemma (PLATE 9, FIGURE I8). The wall cutting off 
the mother-cell is not at right angles to the surface of the leaf but 
is oblique to it and lies in such a way that the cell cut off partly 
overlaps the stalk-cell when looked at from above. The mother- 
cell then divides into two unequal cells by a second oblique wall 
and this is cut by a third oblique wall. The young gemma now 
consists of three cells: two of these, the basal cells, connect the 
gemma with the stalk-cell and apparently undergo no further 
divisions ; the third is a wedge-shaped cell, entirely free from the 
stalk-cell and beginning at once to function as an apical cell. As 
the development of the gemma continues, the basal cells lengthen 
and grow back over the surface of the leaf, in this way displacing 
the region of attachment to the stalk-cell until it comes to lie at 
some little distance from the margin of the gemma on its ventral 
surface (FIGURES 19, 20). While these changes are going on in the 
basal cells, the apical cell is undergoing a series of rapid divisions 
and soon gives rise to a circular cell-layer composed of a consid- 
erable number of small cells. In the subsequent growth of the 
gemma these cells increase markedly in size, but their growth is 
apparently unaccompanied by further cell divisions, the apical cell 
itself eventually becoming indistinguishable from the other mar- 
ginal] cells (FIGURE 21). 
The adult gemma is not flat but is shaped very much like a 
watch-glass and lies with its convex surface turned toward the 
leaf. The cells composing it show very little differentiation, but 
the marginal cells are a little smaller than the others and their 
