286 
Evans .— Vegetative Reprodiicticni in Metzgeria. 
condition persists for a short distance in the basal region (Fig. n, b), but 
except for this the gemma is only one cell thick throughout its entire 
extent. The hooked hairs are sometimes truly marginal, but are more 
likely to be displaced to either surface. They usually occur singly, but are 
occasionally found in pairs. The gemmae show no evident indications of 
dorsiventrality. 
The germination of a gemma exhibits no unusual features. It gives 
rise to a flat thallus which gradually becomes broader, the new marginal 
Fig. ii. M. vivipara. a. A gemma about ready to separate, x 80. b. Base of a gemma, 
x 300. c. Portion of a young thallus developed from a gemma, showing dichotomous branching, 
x 80. 
hairs tend to be straight instead of hooked, and many become displaced to 
what may now be considered the postical surface, other hairs arise on the 
same surface at some distance from the margin, and finally the costa 
appears and increases more and more in complexity. In some cases the 
development of postical surface hairs is deferred until the rudiments of the 
costa have become evident. A tendency to dichotomy frequently becomes 
manifest, not only in the gemma itself, but also in the young thallus while 
it still consists of a single layer of cells (Fig. 11, c). A similar dichotomy 
has already been described in M. quadriseriata, where, however, it occurs 
as a rather unusual exception. Both the gemmae and the young plants 
