610 LICHENS UNDER THE MICROSCOPE. 
and in this way many lichens on which apothecia rarely or 
never occur, are multiplied. In some Verrucarias there are 
small gonidia, called hymenial gonidia, included in the 
hymenium. 
The gelatinous substance which is found in the thallus is 
called lichenine. It is of a starchy nature. In many crus- 
taceous lichens, oxalate of lime is present in considerable 
quantities, and may be easily recognized by its octahedric 
erystals. Phosphate of lime, salt, sugar, oil, with various 
peeuliar acids, also occur, but not in great abundance. 
Having thus viewed the principal features of the lichen 
thallus, let us now turn our attention to its organs of fructi- 
fication. On looking at the lichen (Theloschistes) already 
selected, we shall see its surface covered with small round 
disks of nearly the same color as the thallus. These are the 
apothecia (Fig. 144), and contain the spores, the reproduc- 
tive organs of the plant. Making a thin perpendicular sec- 
tion of one of these, and placing it under our lens, we shall 
see that it is surrounded by a margin containing gonidia like 
the thallus. The interior (Fig. 145) is composed of a mass 
of parallel filaments, called paraphyses, among which are the 
asci, or Spore-cases. This interior portion is called the hy- 
menium. That part which contains the paraphyses and asci 
is called the thalamium, and the portion below it, the hy- 
pothecium. 
Those lichens whose fruit has an open disk, are called 
gymnocarpous. The margin of the disk is called the exci- 
ple. When formed from the thallus, and containing gonidia, 
it is called a thalline exciple ; when otherwise, a proper exci- 
ple. The thalline exciple is usually pale, yellow, brown, 
red, or of the same color as the thallus, though it often 
blackens. The proper exciple is either black, as in Lecidea, 
or colored, as in Biatora. But in many lichens with a thal- 
line exciple, it often assumes a biatorine form. The exciple 
is sometimes double, asin Gyalecta. The color of the disk 
varies greatly, being flesh-colored, yellow, red, brown, OY 
