FUNGI. 25 



but also for certain parts of the tree. A leaf or needle 

 fungus, for example, will never attack the heart wood 

 or the roots of a tree. 



The fungous plant proper consists of extremely deli- 

 cate threads (hyphse), mostly invisible to the naked eye, 

 unless they appear in masses, for instance, in shape of 

 white felts in decayed wood. The hyphse of a fungus 

 are called, collectively, mycelium (PI. VIII). The 

 hyphse of the parasitic fungi we are mostly concerned 

 with live inside the tree, in the tissues of the trunk, roots, 

 or leaves. They grow and produce fruiting bodies 

 (sporophores). As the name indicates, these are not 

 the fungus itself, but what may be termed its " fruit," 

 producing " spores." The conch or stool on the trunk 

 of a Douglas fir, for example, is not the fungous plant ; 

 this lives in the interior of the tree, and the conch is 

 nothing but the fruiting body. 



The fruiting bodies are only formed after the fungus 

 plant (mycelium) in the host tree has reached a cer- 

 tain maturity at the cost of the tissues (cells or cell 

 contents) they live in. The fruiting bodies of some 

 fungi are formed annually; others are perennial. -The 

 mycelium of a fungus may be likened to the root system 

 of the higher plants, which pervades a given volume 

 of soil according to the species and the state of devel- 

 opment of the plant. In the same way in which the 

 root system of a mature grass plant, for instance, takes 

 its raw food and water from an infinitely smaller vol- 

 ume of soil than that of a mature yellow pine, the 

 mycelium of a needle-inhabiting fungus occupies a 

 very much smaller volume of host tissue than that of 



