2 76 Evans .— Vegetative Reproduction in Metzgeria. 
rhizoids; and slime papillae make their appearance in the region of the 
growing point, always on the postical surface. With the further develop¬ 
ment of the costa the differentiation of the thallus becomes complete, and 
the characteristic branching by forking soon begins. The young plant is 
strongly subject to the phenomenon of reversion. Even after the costa has 
become distinct it is not unusual for a thallus to continue its development 
as a simple layer of cells. It is also very prone to develop secondary 
gemmae (Fig. 3), and it sometimes does this before it has begun to show 
any signs of differentiation. In fact, secondary gemmae sometimes arise 
on a primary gemma which is still attached 
to the parent thallus. The secondary 
gemmae are essentially like the primary, 
passing through the same course of de¬ 
velopment and becoming separated in the 
same way. 
Metzgeria uncigera, sp. nov. Pale 
green, growing in depressed mats : thallus 
prostrate, repeatedly dichotomous, well- 
developed branches about i-2 mm. wide 
and from 1-5 to 2-5 mm. long between 
two successive forks, plane ; costa bounded 
both antically and postically by two rows 
of cortical cells ; wings usually from fifteen 
to twenty cells broad, the cells thin-walled 
throughout, averaging about 28x21// and 
not varying much in size in different parts 
of the thallus ; hairs few and irregularly 
scattered, restricted to the margin and to 
the postical surface of the costa, the 
marginal hairs averaging about 70 // in 
length, usually straight but sometimes 
hooked at the apex, occurring singly, 
sometimes truly marginal, but often slightly 
displaced to the postical surface: inflorescence dioicous : $ branch broadly 
orbicular-obovate, about 0*15 mm. long, with scattered marginal hairs: 
gemmae marginal, ligulate, one cell thick throughout, without a distinct 
stalk, apical cell single, hairs marginal or slightly displaced to one surface, 
hooked at the tip : remaining parts not seen. 
Fig. 3. M . uncigera . Apical portion 
of a thallus developed from a gemma 
and bearing new gemmae along its margin, 
x 40. 
On trunks of trees. Porto Rico: Mount Morales, near Utuado, 
March 19, 1906 (Howe, No. 1128). 
The present species is closely related to M. furcata, although the costa 
has only two rows of cortical cells on the postical surface instead of four. 
It is distinguished by its smaller cells and by the absence of surface hairs 
on the wings of the thallus. Its gemmae, also, are less differentiated and 
fail to show a costa even when large and well developed. The relationship 
of M. uncigera to M. hamata , where the costa is built up on essentially the 
