FUNGI. 227 



tree roots. They are attached to the outer cells of the 

 young roots, and penetrate the surrounding soil. The 

 tree takes from them nitrogenous and other matters 

 obtained by the fungus from dead leaves, etc. ; and 

 they, in return, obtain a share of sugary material from 

 the root cells. This fungus servant, or mycorhiza, is 

 found on almost all trees and, indeed, on plants 

 of every description, except willows, grasses, and 

 some others found especially in watery places, where 

 there is no lack of organic matter. There is, however, 

 some doubt as to the exact nature of this fungus 

 servant, or mycorhiza. 



Agaricus is by far the largest genus. Lactarius is 

 very similar to it in appearance, but has a whitish 

 milky juice ; and there are several other genera which 

 are difficult to distinguish from Agaricus. 



Polyporus is easily recognised from the fact of its 

 under surface being dotted with numerous pores or 

 holes, and also from its position, generally on the 

 trunks of old trees. Sometimes the fungus is hoof-like, 

 or bracket-shaped. P. versicolor is easily recognised 

 by the bands of different colours on the upper side of 

 the bracket. Other Polypori are irregular, corky, or 

 almost woody masses found at the base of stumps, or 

 on wood. One of them- Pofyporus betulimis, makes an 

 excellent razor strop. All of them might be utilised as 

 charcoal for gunpowder manufacture, but the difficulties 

 involved in collection on a large scale are probably too 

 great. Most of the Polypori attack decaying wood or 

 are parasitic on trees, but a few may be found on the 

 ground. 



The Basidiomycetes contain besides the Hymenomy- 

 cetes (Mushrooms, Polyporus, Boletus, etc.) another 

 group, Gastromycetes. This group differs from the 



