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-hyphre, 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 paraphyses, so as to form a layer that lies either on the surface 



FIG. 486. Examples of various algse which are employed as the gonids of lichens : 

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

 spore, s, of Physcia parietina, the germ- tube of which adheres closely to Proto- 

 coccus viridis ; B, a filament of Scytonema withhyphae of Stereocaulonramulosus 

 twined round it ; C, from the thallus of the lichen Phijsma clialaganum a hyphal 

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

 the lichen Synalissa sympliorea the gonids are the alga Glceocapsa ; E, from 

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

 rounded by the hyphae, are the cells of Protococcus. After Bornet. A, C, D, E, 

 magnified 950 ; B, 650 times. (From Goebel's ' Classification and Special Mor- 

 phology of Plants.') 



of apotheces, or is completely enclosed within perit/ieces. 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 pollinoids or ' spermatia ' 

 and the female trichogyne. These pollinoids are produced within 



