188 



BOTANY. 



body. Experiments have shown ' that these filaments 

 will not grow for any great length of time unless 

 they come into contact with a green plant of the proper 

 species, to which they become attached, growing rapidly 

 and surrounding them. On the other hand, in the moist 



Fig. 111.— Sections of gelatinous Lichens (CoUema), showing (in A) a 

 carpogone, c, with its projection, d. and (in B) a cavity (spermogone) 

 emitting sperm-cells (spermatia). The gonidlahere (b, &) are species of 

 Nostoc. Highly magnified. 



tissues thus formed the green plants find protection and 

 ample opportunity for growing. There is thus an associa- 

 tion between these plants which is mutually beneficial 

 (symbiosis). The lichen lives parasitically upon the green 

 plants, to which it in return furnishes shelter and moisture. 

 347. 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 (Pig. Ill, A, c, d). Fertilization takes 

 place by means of minute cells (sperm-cells, or spermatia), 

 which are produced in countless numbers in cavities {sper- 

 mogones) in the lichen-body. The sperm-cells come in 



