290 Evans .— Vegetative Reproduction i?i Metzgeria. 
indications of dorsi-ventrality. Where the two basal cells are situated the 
margin is either truncate or more or less retuse. The numerous hairs are 
all truly marginal and always occur singly. They are about three times as 
long as the cells of the gemma and are hooked at the apex. The two 
apical cells are situated in the outer portions of the symmetrical halves. 
A typical gemma is about 0-2 mm. long at the time of separation and 
measures about eight cells across the middle. 
When a gemma germinates normally each of the apical regions 
develops a strap-shaped thallus one cell thick and about eight cells wide 
(Fig. 13, b). These two thalli diverge at a wide angle, and continue to 
produce an abundance of scattered hooked hairs along the margin similar to 
those on the gemma. In some cases only one of the apical cells continues 
its divisions, and under these conditions only one thallus is developed, the 
germinating gemma thereby losing its symmetrical appearance. A similar 
result is produced when one of the young thalli grows more rapidly 
than the other. Unfortunately, the later stages of germination could not 
be observed. 
Metzgeria disciformis , sp. nov. 
The plants which bear the gemmae are scarcely modified, and appa¬ 
rently show no marked tendency to limit their growth. The gemmae, as in 
the preceding species, arise without definite order, 
and are sometimes fairly abundant. In the early 
development of a gemma one of the alar cells pro¬ 
jects above the surface in the usual way, but it 
becomes at once the mother-cell of the gemma 
without undergoing one or more preliminary di¬ 
visions. In this respect M. disciformis differs 
markedly from most of the other species which 
bear antical gemmae, but agrees with most of those 
which bear marginal gemmae. When a gemma 
separates it leaves behind an empty cell which 
appears like a perforation of the thallus. The gemmae are often more 
or less strongly tinged with blue, especially when young, a condition 
which seems to be due to a pigmentation of the cell-walls. A mature 
gemma (Fig. 14) is in the form of a concave and circular plate of cells, 
about 0*2 mm. in diameter and measuring about twelve cells across. In 
the basal region it shows a short but distinct stalk, composed of two or 
three cells, and the single apical cell is also clearly apparent. As in 
M. L lebmanniana, the concave surface of the gemma represents the postical 
surface, and the dorsiventrality of the structure is even better marked. 
All around the margin are numerous short and straight hairs, some of 
which are truly marginal, although the majority are slightly displaced to 
Fig. 14. M. disciformis. 
A gemma about ready to 
separate, postical view, x 80. 
