338 



A TEXTBOOK OF THEORETICAL BOTANY 



preferences, while others exhibit biologic races which still further restrict 

 the host range of the Fungus. 



..^ 



Fig. 331. — Inocybe maritima. Fruiting body of the 

 Fungus, which generally occurs on sand dunes 

 associated with Aminophila areuaria. 



Special Features of Fungal Nutrition 



Fungi may be divided, as has been pointed out above, into saprophytes 



and parasites, but the latter group may also be divided into obligate parasites 



and facultative parasites. The former are incapable of growth on anything 



but a living host, and it is concluded that they require their food materials 



in highly elaborated forms, or, in other words, that they have little if any 



power of synthesis. The latter group of facultative parasites, however, are 



also able to grow as saprophytes on artificial media so that they must be able 



to build up their specific carbohydrates and proteins from relatively simple 



organic substances. ]Most can use simple sugars such as dextrose as sources 



of Carbon, and some can use even inorganic materials such as nitrates or 



ammonia as Nitrogen sources. The majority, however, require Nitrogen 



in organic combination, either as amides or amino-acids. The difl^erent 



powers displayed in this connection correspond no doubt to the presence 



or absence of certain necessary enzymes, since it is by means of specific 



enzymes that the nutrients obtainable are altered into assimilable forms and 



subsequently built up into the fungal substances, as well as into the numerous 



by-products of the metabolism. These are peculiarly numerous in Fungi 



and are often, as in the case of toxins, of great biological and economic 



importance. 



