284 



Introduction to Botany. 



Besides multiplying 

 by spores, the toadstools 

 may be disseminated by 

 the separation of bits of 

 the masses of filaments 

 which occupy the sub- 

 stratum ; in this way 

 mushrooms are artifi- 

 cially propagated. 



LICHENS. 



175. Nature of Lichens. 

 The Lichens afford a 

 unique example of para- 

 sitism by Fungi ; for a 

 Lichen is not a distinct 

 plant, but rather a com- 

 munity of Fungus and 

 Algae. The little Pleuro- 

 coccus with which we are 



already acquainted is often associated with a Fungus in 



this way. The Fungus 



undoubtedly derives its 



food from materials man- 

 ufactured by the Algae, 



but at the same time it 



does the Algae no bodily 



harm, except that which 



might result from the tax 



on their industry. It is 



thought by some that 



there is a fair exchange 



of benefits between the 



FIG. 147. 



Trunk of a tree in process of destruction by 

 Fungi. Fungi belonging to the genus Poly- 

 porus growing out from the trunk. Interior 

 of the tree rotten and hollow and used as a 

 nest by owls. 



FIG. 148. 



Different forms of Lichens. 

 a, Parmelia colpodes ; b, 

 Graphis scripta on bark of 

 tree ; the elongated black 

 spots are the Lichens ; c, 

 Cladonia furcata. 



