— 4 6 — 
UCHENS-COLLEMA AND LEPTOQIUM. 
Carolyn W. Harris. 
Collema is a large genus, represented by many species which after 
further study may be divided into several genera, as the spore characters 
are such that this division seems possible. The thallus is foliaceous, in a 
few species fruticose, in some it is small and irregular, in others large and 
flat, but in all it is more or less folded and rugose. Collemas are very gela- 
tinous when moist, very thin in texture. They are generally considered of 
low development but they have some characteristics which are quite com- 
plex. The color varies from a light lead color to a very dark, greenish blue, 
almost black, the under surface is lighter with no rhizoids. The margin of 
the thallus is divided into lobes with obtuse tips. ' The apothecia are usually 
small or medium, frequently very numerous. The color of the disk is red- 
dish brown to dark brown, flat or slightly convex with an entire, crenate 
margin. Collemas are not dependent upon apothecia for propagation as 
soredia are usually present, and it is even possible for a part of the thallus 
to be broken off and form a new plant. They are found on trees, dead 
wood, occasionally on damp rocks. They require much moisture for their full 
development, Are common throughout the United States and Canada. 
Leptogium. The thallus of this genus closely resembles that of Collema; 
it is usually larger and not so gelatinous, more wrinkled and thicker. On 
the under side are fine gray rhizoids in clusters, or there is a fine close nap. 
The apothecia are small with a reddish brown disk, with .a lighter raised 
margin. Soredia are present in many species where no apothecia are found. 
Leptogium is probably only a higher development of Collema; the two 
genera are found in the same localities. The amateur can distinguish these 
genera readily by examining the under surface, in Collema it is devoid of 
rhizoids, in Leptogium they are always present in some form. 
Collema flaccioum Ach. Plate VI. Fig. i. Thallus composed of large, 
round, entire lobes which are folded together, giving a puckered effect; these 
are usually covered with granules of the same color as the thallus which is 
a dark olive green. The margin is undulate and frequently plicate or 
folded. The under side is a dull dark gray, much wrinkled. 
Apothecia, which are not common, are small, scattered and sessile, the 
disk is chestnut, quite flat, with an entire, granulate margin. 
Habitat granite rocks and trunks of old trees; found principally in 
mountainous regions. When moist is very flaccid as the specific name indi- 
cates, when dry it is thin and brittle. 
Collema nigrescens (Huds.) Ach. Plate VI. Fig, 2. The thallus of 
this very pretty lichen is thin, nearly round, very delicate at the margin but 
stronger toward the center where the small apothecia are massed. The 
lobes are entire, round and flexuous, clinging closely to the substratum, but 
when damp can be removed with care. The wrinkles in the thallus are very 
conspicuous giving a pustulate appearance. It is a dark olive green turn- 
ing darker when fully developed; the under side is a little lighter in color 
with deep pit-like radiating wrinkles. 
