STEVENS: DIscoID GEMMAE IN LEAFY HEPATICS 369 
was examined. This showed that the gemmae of the two species 
are essentially alike in their development, form, and method of 
attachment. One immature gemma of C. calcarea, however, was 
found in which the first anticlinal walls had not been displaced 
by the growth of the apical cells (FIG. 1, G). The basal and apical 
quadrants are thus nearly equal, and the gemma as a whole appears 
more like those figured by Cavers. It is very probable that it 
was from such a condition as this that his figures were taken. 
RADULA COMPLANATA. 
In Radula complanata the gemmae are borne on the edges of 
the leaves, frequently at right angles to the leaf surface. A single 
leaf often bears a considerable number of gemmae and it is common 
to find leaves where every cell for a considerable portion of the 
margin has given rise toa gemma. Gemmae are of more frequent 
occurrence in R. complanata than in most species. In fact so 
general is their occurrence that it is comparatively rare to find 
well-developed plants which do not bear gemmae. Moreover, 
it is evident that there can be here no such antagonism between 
the production of gemmae and of sexual organs as has been 
supposed by some writers, for the gemmae are frequently borne 
on the edge of the perianth itself, as well as on the bracts. 
Each gemma arises from a single marginal cell, which projects 
beyond the cells on either side and becomes at once the mother- 
cell of the gemma. This cell as it increases in size secretes a gela- 
tinous substance which may be noted around the edge of the cell. 
The secretion of this gelatinous substance appears to be charac- 
teristic of rapidly growing cells in the gemma and the occurrence 
of gelatinous material in considerable quantity may be taken as 
a rough indication of the region of most rapid cell division (FIG. 2, 
A, C, and D; Fic. 3, A; and Fic. 4, A and C). The gemma 
mother-cell divides first by a periclinal wall (FIG. 2, A). This 
wall is sometimes perpendicular to the surface of the leaf, but is 
more often so inclined that the outer of the two cells, which is 
generally the larger, overlies a portion of the inner cell. The 
outer cell, which gives rise to the main portion of the gemma, 
divides first by a longitudinal wall (F1c. 2, B). The inner cell 
divides later by a longitudinal wall and forms the two-celled basal 
