Evans .— Vegetative Reproduction in Metzgeria. 285 
In rare cases the germination of the gemmae begins while they are 
still attached to the parent thallus, but the process is usually deferred until 
they have become separated. In normal cases, such as the one represented 
in Fig. 10, a, the apical cell of the gemma renews or continues its activities, 
and gives rise to a strap-shaped thallus which is at first but a single cell 
thick and about six cells wide. The margin bears numerous scattered hairs, 
but the young plant shows no further evidences of cell-differentiation and 
no signs of dorsiventrality. As its growth proceeds scattered hairs appear 
on one surface (destined to become the postical), the median cells become 
arranged in two longitudinal rows, and before long divide by walls parallel 
to the surface, thus giving rise to a rudimentary costa (Fig. 10, b). The 
further differentiation of the thallus pursues the normal course. In the 
rare cases where two apical cells are present and functional the gemma 
gives rise to two diverging thalli (Fig. 10, c). Another rare case is shown 
in Fig. 10, D, where the young thallus does not arise from the apical cell 
at all, but from one of the other marginal cells of the gemma. The process 
of germination is sometimes modified by reversion, as illustrated in 
Fig. 10, E, where the young thallus is only two cells wide. It may also be 
complicated by the formation of new gemma, which invariably arise on the 
margin of the young thallus instead of on its surface. In Fig. 10, F, where 
two such marginal gemmae are shown, their formation was apparently 
induced by the death of the apical cell of the thallus, but they sometimes 
occur while the apical cell still continues active. The marginal gemmae 
thus produced differ from the antical gemmae of the species, and bear a 
marked resemblance to the marginal gemmae described for some of the 
preceding forms. 
Metzgeria vivipara , sp. nov. 
The gemmae, as in M. crassipilis , are borne upon branches which show 
few or no signs of specialization. When they are produced in great 
abundance the growth of the gemmiparous branch tends to be limited, but 
this tendency is not very apparent and seems to be easily overcome. The 
projecting alar cell which is to form a gemma first divides by several 
longitudinal walls before the transverse walls which mark off the young 
gemma make their appearance. As a result of this the gemma upon 
separating leaves behind a patch of three to five small thallus cells instead 
of a single larger cell. The mature gemmae are very similar to the 
marginal gemmae of M. uncigera. Each one is a flat strap-shaped thallus 
with a single apical cell and numerous hooked marginal hairs (Fig. 11, a). 
It measures about o-6 mm. in length by 0-15 mm. in width and is usually 
from six to eight cells across. Towards the base there is a gradual tapering, 
and the three to five basal cells, which form a short and poorly defined 
stalk, are commonly arranged in two layers. Sometimes the two-layered 
