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FAMILIES AND GENERA 317
superficial or embedded. The genera are arranged according to spore
characters :
Spores elongate, 2- or more-septate.
Spore cells cylindrical, colourless i. *Pleurotrema Miill.-Arg.
Spore cells globose-lentiform.
Spores colourless 2. *Plagiotrema Miill.-Arg.
Spores brown 3. *Parathelium Miill.-Arg.
Spores muriform.
Spores colourless 4. *Campylothelium Mull.-Arg.
Spores brown 5. *Pleurothelium Miill.-Arg.
IX. TR YPETHEL IA CEA E
This and the following two families are distinguished by the pseudo-
stroma or compound fruit, a character rare among lichens, though the true
stroma is frequent in Pyrenomycetes in such genera as Dothidea, Valsa, etc.
The genera are crustaceous and corticolous and occur with few exceptions
in tropical or subtropical regions, mostly in the Western Hemisphere.
Several grow on officinal bark (Cinchona, etc.). Algal cells are Trentepohlia.
As in many tropical lichens, the spores are large. The genera are based
chiefly on spore characters, on septation, and on the form of the spore
cells :
Spore cells cylindrical or cuboid.
Spores colourless, elongate, multi-septate i. *Tomasiella Miill.-Arg.
Spores colourless, muriform 2. *Laurera Rehb.
Spores brown, muriform 3. *Bottaria Massal.
Spore cells globose-lentiform.
Spores colourless, elongate, multi-septate 4. *Tr\ pethelium Spreng.
Spores brown, elongate, multi-septate 5. Melanotheca Miill.-Arg.
X. ASTROTHELIACEAE
The perithecia are either upright or inclined, and occur usually in
radiate groups. They are free or united in a stroma, and the elongate
ostioles open separately or coalesce in a common canal. The genera are
all crustaceous, with Trentepohlia gonidia. They are tropical or subtropical,
mostly in the Western Hemisphere; but species of Parmentaria and Astrothelium
have been recorded also from Australia.
The spores are all many-celled and the form of their cells is a generic
character :
'
Spores elongate, multi-septate.
Spore cells cylindrical
Spore cells globose-lentiform.
I- *Lithothelium Miill.-Arg.
colourless 2. *Astrothelium Trev.
Spores
Spores brown 3- *Pyrenastrum Eschw.
Spores muriform.
Spores colourless 4- *Heufleria Trev.
Spores brown 5- *Parmentaria Fe'e.