n 



8 Mycologia 



of these and other species growing on standing trees are usually 

 found nearer the earth. 



It is very evident that the occurrence of fungi, particularly 

 the fleshy species, in elevated regions is closely correlated with the 

 ratios of evaporation and precipitation. The excessive precipita- 

 tion in the form of rain and snow is counteracted by the rapid 

 evaporation from all substrata except in the more protected places 

 or on north slopes. The influence of topography in this respect 

 tends to produce a wide variation in the fungous flora in very 

 narrow confines. Rounded peaks have many exposures. Con- 

 sequently, fungous associations on the same mountain may be 

 widely different. Though trees may be present on exposed wind- 

 swept sites, all classes of fungi except a few perennials or species 

 with special adaptation are usually absent. Those that do occur 

 on such sites, if not found to be entirely different species from 

 those occurring in protected exposures where the snow collects, 

 are often so modified that, they could well be classed as biological 

 forms. Some of the fungi usually characterizing exposed sites 

 are Lentinus lepideus Fr., Lenzites sepiaria (Wulf.) Fr., Poly- 

 stictus hirsutus Fr., Polyporus leucospongia Cke., and certain 

 Patellea species. The greater amount of snow on protected sites 

 prevents the radiation of heat from the substrata, hence prevents 

 evaporation and desiccation and usually promotes the develop- 

 ment of certain fungi, particularly the more fleshy wood-destroy- 

 ing species. On the other hand, annual sporophores may be 

 entirely absent under the more extreme conditions owing to the 

 fact that snow shortens the period of vegetative growth or the 

 weight and movement of snow is too great to be sustained. 



Any factor that influences the cellular and chemical develop- 

 ment of the wood of a tree may influence the growth of some 

 wood-destroying fungi, hence their distribution. Aside from the 

 moisture relation which is always a factor in promoting the 

 growth of fungi, the influence of elevation on the chemical and 

 anatomical structure of forest trees is a well known phenomenon 

 and in a measure determines their predisposition to disease. Ac- 

 cording to Weber 4 the organic content of larches and beeches 



4 Einfluss des Standortes auf die Zusammensetzung der Asche von Larchen. 

 Allgem. Forst.- u. Jagdzeitung. P. 367. 1873. 



