442 



FUNGOUS DISEASES OF PLANTS 



great majority of the plants commonly known as mushrooms, toad- 

 stools, punks, etc., plants exceedingly variable in size, form, and 

 texture. The mycelium is generally abundant, and it is made up 

 of relatively minute hyphse in loose wefts or flocculent masses, 

 sometimes closely united into bands or strands (rhizomorphs), and 

 often perennial. Sclerotia also occur. The fruit body varies from 

 what is merely a close hyphal weft to bodies most diversely consti- 

 tuted, and very complex in structure (sporophores). In fact, the fruit 

 body may be felt-like, pellicular, leathery, fleshy, corky, or woody 

 in texture. Conidial stages of several types are present in some 

 families, but in this group these imperfect forms have not the same 

 relative significance in propagation as in the Ascomycetes. The 

 mycelium of a majority of the parasitic or wood-destroying species 

 may be grown in artificial cultures in the laboratory. Frequently 

 the best growth is obtained when such materials as dead wood, 

 decayed leaves, and rich soil are substituted for the usual media. 



The families and genera here to be considered consist of solid 

 sporophores, briefly characterized as follows : 



1 . Thelephoracece. The hy menial surface is more or less smooth. 

 Sporophores are skin-like, gelatinous, or woody in texture, spread 

 out over the surface of the substratum (resupinate), shelving, 

 stalked, or considerably branched. Corticium and Stereum are 

 important genera. 



2. Hydnacece. The hymenial surface is usually spread over 

 tooth-like divisions of the sporophore, the latter, however, some- 

 times wart-like or even more or less briefly plate-like (lamelliform). 

 The sporophores are very diversely formed. The genus Hydnum 

 alone will be considered. 



3. Polyporacecz. The hymenial surface is generally spread over 

 the inner surfaces of pores or narrow tubes, sometimes, however, 

 over folds or shallow depressions between vein-like reticulations, 

 occasionally more or less lamelloid. The sporophores are diverse, 

 generally tough, often very large. Those most important in the 

 production of tree diseases are typical pore-bearing species, which 

 may be assigned to one of three closely related genera, Fomes, 

 Polyporus, and Trametes. 



4. Agaricacecz. The hymenial surface is confined to radial 

 plates or lamellae, the latter, however, sometimes in the form of 



