(by AND BRANCH DISEASES AND INJURIES 69 



Ising the wood-rots, the characters of the fruitlng-bodies 

 hve to identify the causal fungus, if they are definitely as- 

 'sociated with the rot. The correct determination of the dif- 

 ferent species of bracket-fungi is, however, not easy in some 

 cases. The number of species of annual forms represented in 

 the United States is greater than that of the perennial forms. 

 A generic distinction between the annual and perennial forms 

 is recognized and they have been named respectively Po- 

 lyporus (po-lip'-pore-us) and Fomes (fo-meez). Other genera 

 have been split off from these two, which probably represent 

 a more natural classification. Since, however, the simpler 

 and more artificial classification is still used by laymen and 

 most scientists, the genera Polyporus and Fomes are used in 

 the discussion of the wood-rot fungi in this book. For a 

 synonymy of polypore names, see the appendix, page 364. 

 The species of Polyporus usually produce a more or less fleshy 

 or corky fruiting-body which is soon destroyed by insects or 

 decay and rarely functions in producing spores for more than 

 the single season. The species of Fomes, on the other hand, 

 form hard, woody structures which develop a new layer of 

 tubes on the under surface each year as long as food material 

 is being obtained by the mycelium, in its advance into normal 

 wood. In this manner the size of the fruiting-body increases 

 yearly and its age may be determined by counting the layers 

 of tubes when the fruiting-body is split perpendicularly. 



Dissemination of the spores. 



The spores of the bracket-fungi are borne in groups of four, 

 each on a tiny spine, ^at the ends of branches of the mycelium 

 which project from the inner sides of the tubes. When mature, 

 these spores are shot from their attachment with just enough 

 force to bring them to the center of the tube, and then they 

 drop out of the open end at the bottom. The wind, or even the 

 slightest breeze, serves to carry the spores for long distances, 



