Evans .— Vegetative Reproduction in Metzgeria. 283 
secretes a gelatinous layer, just as in M. uncigcra, and this is followed by 
a rupture of the outer wall (Fig. 8, c). The projecting cell then divides 
by a wall approximately parallel to the surface of the thallus, and the upper 
cell thus cut off becomes the mother-cell of the future gemma. In some 
cases the projecting cell divides first by a perpendicular wall, and then, 
when the horizontal wall is formed, the rudiment of the gemma consists of 
two cells. Even when it consists of a single mother-cell, a condition which 
seems to be the more typical, it is quickly divided by a longitudinal wall 
Fig. 9. AT. crassipilis. a. A very young gemma with two apical cells. X300. B. A typical 
gemma about ready to separate, x 300. c. Section through a young gemma and adjacent cells of 
thallus. x 300. D. Section through a similar region after the gemma has escaped. x 300. 
E. Surface view of a ruptured cell, x 400. 
into two cells. Beyond the two-celled stage the development of the gemma 
is subject to further variation. The two cells first divide two or three times 
by cross walls, thus giving rise to a rounded structure composed of two rows 
of cells side by side. Some of these cells then divide by periclinal walls 
(Fig. 8, d and e), and before long one or two cells acting as two-sided 
apical cells make their appearance (Figs. 8, F, and 9, A). The apical cells 
are derived from the terminal cells of the original two rows, and it usually 
happens, even when two are formed, that only one continues to function. 
The result is that the mature gemma, except in very rare instances, has 
a single apical cell. At the time of separation the gemmae vary consider¬ 
ably in size, but the example represented in Fig. 9, B, may be regarded as 
fairly typical. Such a gemma is in the form of an orbicular and flat plate 
