262 



ESSENTIALS OF BOTANY 



and some of them parasitic. A few may live in either 

 fasliion at will. The mycelium through which the plant 

 obtains its nourishment is often so fine and inconspicuous 

 that it escapes notice, and the fruiting portion, is com- 

 monly thought to spring directly from the earth, bark, 

 wood, or other substratum to which it is attached. The 



reproduction is wholly asexual. 

 Gill fungi are of consider- 

 able economic importance. A 

 good many are edible (though 

 others which resemble them are 

 actively poisonous). Such par- 

 asitic species as Armillaria mel- 

 lea (Fig. 185) are very injurious 

 to timber. This fungus sends 

 its mycelium through the bark 

 or between the bark and wood 

 of trees and often causes the 

 death of the host. 



A large shelf -fungus (2Va- 

 metes JPini) of a closely related 

 group (Fig. 184) is very destruc- 

 tive to trees of the Pine famil}-. 

 The lack of sexual reproduc- 

 tion in organisms as compli- 

 cated as the gill fungi seems 

 to be evidence that these forms are degenerating. The 

 same conclusion is suggested by the occurrence of what 

 appears to be imperfect reproductive apparatus of Puccinia 

 on the upper surfaces of infected barberry leaves. There 

 is much other evidence of the same sort, and it all agrees 

 with the supposition that fungi are degenerate descendants 



Fig. 187. Part of the Preceding 

 Pigure. (x about 300.)- 



C, layer of cells immediately under 

 the hymenium. s, 5', s", three 

 successive stages in growth of 

 spores. 



