CHAPTER IV 



GENERAL RELATIONS TO ENVIRONMENTAL FACTORS 



BENECKE, W. Allgemeine Physiologic der Ernahrung der Schizomyceten 

 und der Eumycetem (Stoffwechsel). Lafar's Hdb. d. tech. Mykologie 1 : 

 303-427. 



I. SAPROPHYTISM AND PARASITISM 



Since the fungi are those classes of plants low in the series with 

 respect to morphological complexity which possess no chlorophyll, 

 they are unable to utilize the carbon dioxid of the air, and like in- 

 sects and other animals they require their carbon in organic com- 

 binations. They are accordingly associated with organic matter, 

 living or dead. The plant pathologist devotes primary attention to 

 those fungi inducing injuries sufficient to be termed plant diseases. 

 Interest is, of course, attached also to any parasitic species ; that 

 is, to any which may penetrate and develop within or upon the 

 tissues of another plant, but the nature and extent of the disturb- 

 ances which result offer the special problems and make necessary 

 the special field of the pathologist. 



The habitats of the majority of the fungi are situations in which 

 organic matter is available through the decay of dead things. In- 

 deed the fungi take a prominent part in decay, or the return of 

 organic matter to more elementary combinations. Forest and field, 

 therefore, abound in species, whether evident or not to the popu- 

 lar eye. The fungi associated with decaying materials only are 

 termed saprophytes (metatrophs}. Theoretically, the pathologist is 

 not concerned with this class of organisms. On the other hand, 

 a very considerable part of the fungi obtain their organic nutrients 

 by penetrating a living organism as host and growing in inti- 

 mate association with its body. Such fungi are termed parasites 

 (paratrophs}. The parasitic fungi are, for the most part, parasitic 

 upon plants, although small groups are confined very largely to 

 insects, and a few species affect higher animals. 



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