650 



FUNGI 



weave themselves round them, and enclose them in their hyphal 

 tissue. But not only this : the algal constituent of the lichen 

 appears also to derive benefit from, and to be nourished by, the 

 fungus-hyphse, affording an example of the singular kind of mutual 

 dependence known as commensalism or symbiosis (fig. 486.) The 

 formation of sexually produced 'spores' usually takes place in asci 

 arranged vertically in the midst of straight elongated sterile cells 

 termed paraphi/ses, so as to form a layer that lies either on the surface 



FIG. 480. Examples of various alga? which are employed as the gonids of lichens : 

 // indicates always the hypha of the fungus ; g' the gonid : A, germinating 

 spore, s, of Pliyscia parietina, the germ-tube of which adheres closely to Profo- 

 coccus viridis ; B, a filament of Scytonema withhypha? of Stereocaulon ramulosus 

 twined round it ; C, from the thallus of the lichen Phi/sma clialatjanum a hyphal 

 branch is entering a cell of the Nostoc filament (gonid) ; D, from the thallus of 

 the lichen Sy-iialissa symphorea the gonids are the alga Gloeocapsa; E, from 

 the thallus of the lichen Cladonia furcata ; the gonids, which are being sur- 

 rounded by the hypha?, are the cells of Protococc.us. After Bornet. A, C, D, E, 

 magnified 050; B, 650 times. (From Goebel's 'Classification and Special Mor- 

 phology of Plants.') 



of apotheces, or is completely enclosed within jieritliecrs. Each of the 

 asci contains a definite number of ascospores, usually eight, which 

 are projected from the receptacles with some force ; and their 

 emission, which seems to be due to the different effects of moisture 

 upon the several layers of the receptacle, is often kept up con- 

 tinuously for some time. The formation of these asci, as in the 

 case of the ordinary Ascomycetes, is probably the result of a sexual 

 union which takes place between The male /lollinoids or ' spermatia ' 

 and the female lriclin<n/iie. These pollinoids arc produced within 



