BASIDIOMYCETES. 



169 



not only by the fruit-bodies, but also by the more vigorous growth 

 and darker colour of the grass upon these spots. 



Some species are parasites. An example is presented by Armil- 

 laria mellea, a remarkable and very destructive Fungus in woods and 

 forests (Figs. 176, 177). In addition to the filamentous, white mycelium, it 

 has also black, or black-brown, horny, root-like mycelium-strands (rhizomorpha) 

 which were formerly 



were 



considered to belong to 

 a special genus of Fungi 

 described under the 

 name " Rhizomorpha." 

 The mycelium lives 

 parasitically on the Con- 

 ifers and other trees, 

 forcing its hyphas into 

 the bark and between 

 the bark and wood, and 

 thence penetrating into 

 the wood so that the 

 tree is very severely at- 

 tacked. It may also 

 live saprophytically, and 

 clusters of fruit-bodies 

 are often found on old 

 stumps and stems, on 

 old timber, and in the 

 rich soil of woods. The 

 rhizomorpha, living un- 

 derground, can extend 

 for considerable dis- 

 tances and infect the 

 roots of neighbouring 

 trees, and spreads in 

 this way the diseases 

 known as " Harzsticken " 

 and "Bark -Canker," 

 which are very destruc- 

 tive to young trees. 



J 



Fie. 174. Psalliota campestvls. A Tangential section of 

 pileus showing lamellfe (!) B Portion of gill more highly 

 magnified ; t trama ; hy hymenium with basidia and basidio- 

 spores ; sh, sub-hymenial layer. C A portion of the same 

 more highly magnified ; s' s" s'" s"" various stages in the 

 development of basidiospores ; q paraphyses. 



The chief charac- 

 teristics by which 

 the numerous genera 

 are separated are 

 the presence or the absence of the two kinds of veils, the nature 

 of the fruit-body, the form, branching of the lamella?, and their 

 position and relation with respect to the stem, the shape of the 



