284 Evans: HEPATICAE OF PUERTO RICO 
cells of the younger segments project, while in L. Goebelii the cells 
bounding the median wall are the only ones affected. In gemmae 
with marginal denticulations it is always certain special cells that 
project and these are always definite in position. The outer cell 
of the youngest segment is the one most certain to show this 
condition, as in Aphanolejeunea microscopica, but it is not usual 
for this cell to be the only one that projects. In A. exigua, for 
example, the two basal cells and the opposite one on one side also 
project, and this statement will apply equally well to Cololejeunea 
diaphana and Leptocolea cuneifolia, where more segments are cut 
off. 
The remarkable organs of attachment are fully described by 
Goebel in the case of Leptocolea Goebeliit. They represent marginal 
cells which project at right angles to the two surfaces of a gemma. 
At their extremities they secrete a slime which enables the gemma 
to attach itself to the substratum. These organs of attachment 
are not found in all species and are most frequent in the epiphyllous 
species of the tropics. Of the sixteen species studied by the writer 
seven develop such organs, while the others lack them completely. 
When present they are not only constant in number for a given 
species but also constant in position. In Leptocolea Goebelii and L. 
ovaltfolia four organs of attachment are developed; in L. ceatocarpa, 
L. scabrifolia, L. cuneifolia, Cololejeunea diaphana, and A phanole- 
jeunea exigua there are only three. When four are present two 
are developed from the basal quadrants and two from the first 
segments cut off from the apical quadrants. In each of these a 
periclinal wall is first formed in the usual way and then the outer 
cell divides again by an anticlinal wall. Of the two marginal 
cells thus formed the one farther from the median wall becomes 
modified into the organ of attachment. When only three organs 
are present two are developed from the basal quadrants, which 
divide in the way just described.* The third is formed from the 
first segment on one side. This divides by the usual periclinal 
wall and then the outer of the two cells thus formed becomes 
modified into the organ of attachment without undergoing a pre- 
liminary anticlinal division. For this reason the organ is situated 
* In L. ceatocarpa the division goes one st p farther, the cells which would natur- 
VW = re 34 . Fo PM's . . . . . 
any v d 1 v & h fi d d g by per iclinal walls. 
Sie eal Sheen eet ee a eae 
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