282 Evans .— Vegetative Reproduction in Aletzgeria . 
by four cortical cells. It differs further in its larger alar cells, in its longer 
marginal hairs which are slightly, or not at all, displaced to the postical 
surface, in its lack of postical hairs on the wings, and in its broader and 
less differentiated gemmae. 
Metzgeria crassipilis, (Lindb.) Evans. 
The antical gemmae found in M. crassipilis and its allies are on the 
whole more highly specialized than the marginal gemmae just described. 
Although they are sometimes 
borne in great abundance 
many of the plants fail to 
produce them altogether. 
The range of M. crassipilis , 
so far as known, extends 
from Vermont to North 
Carolina and Tennessee. The 
present study is based almost 
entirely on material collected 
by J. K. Small, on Blowing 
Rock Mountain, North Caro¬ 
lina, in 1892 (No. 31). The 
same material has served 
for the accompanying figures. 
The gemmiparous branches 
differ very slightly from or¬ 
dinary branches and show 
no marked indications of 
having their growth limited. 
The only important modi¬ 
fication which they show is 
an increase in the number of 
cortical cells along the antical 
surface of the costa. On 
normal branches these cells 
are arranged in two rows; 
on gemmiparous branches 
the number of rows varies 
from two to four (Fig. 8, A 
and b). The gemmae are not 
developed in definite order 
and sometimes occur so close together that they overlap as their size 
increases. Each one arises from a single alar cell which first of all projects 
above the surface of the thallus. In this process the protoplast of the cell 
Fig. 8. Af. crassipilis. A. Portion ot a gemmiparous 
branch, x 50. b. Cross section of a gemmiparous branch, 
x 50. C-F. Early stages in the development of gemmae, 
x 300. 
