168 BOTANY. 
mersed in cavities which show only as blackish lines or 
dots on the surface of the lichen-body. 
352. The spores germinate by sending out one or more 
tubes which develop directly into the ordinary filaments of 
the lichen-body. Experiments have shown that these fila- 
ments will not grow for any great length of time unless 
they can come into contact with a protophyte of the proper 
species to which they can become attached. The lichen- 
filaments then grow rapidly and surround the protophytes, 
and in the moist tissues thus formed the latter find protec- 
tion and ample opportunity for growing. There-is thus an 
Fie. 98.—Sections of gelatinous Lichens (Collema), showing (in A) a carpogone, 
c, with its projéction, d. and (in B) a cavity (spermogone) emitting sperm-cells 
(spermatia). ‘The gonidia here (b, b) are species of Nostoc. Highly magnified, 
association between these plants which is mutually bene- 
ficial. The lichen lives parasitically upon the protophytes, 
to which it in return furnishes shelter and moisture. 
358. We know very little as to the sexual organs of 
lichens. A few years ago Stahl discovered them in Colle- 
ma, a low form of gelatinous lichens. The carpogone is a 
tightly coiled spiral filament, which sends up a prolonga- 
tion to the surface (Fig. 93, A, ¢, d ). Fertilization takes 
