2. The Composition 



of 

 Fungus Cells 



u 



T 



nder this head are considered those constituents 

 which as a class if not individually are common to most or all fungi. 

 Materials which are found only in some species are discussed, if sig- 

 nificant, in the section on metabolism; thus, sugar alcohols and carote- 

 noids do not occur in the mycelium of all fungi and so are not included 

 here, but are considered in, respectively, Chapters 5 and 6. Known 

 vitamins produced by fungi are reviewed in Chapter 10. 



The theoretical significance of chemical composition is somewhat 

 limited. It will be seen that, within bounds set by the metabolic 

 capacities of the species, the composition varies widely with the en- 

 vironment. The quantities of fat, carbohydrate, ash, wall material, 

 and total nitrogen are all more or less responsive to the culture me- 

 dium. 



In composition, the principal difference between fungi and bacteria 

 is in the high chitin content of most fungi. Chitin is present in the 

 bacteria (176); the green algae do not have chitin walls. Absence of 

 chitin in the Oomycetes, discussed below, in turn suggests a polyphy- 

 letic origin of the true fungi. A second difference between fungi and 

 bacteria is also quantitative rather than absolute: lipid accumulation 

 is more common and attains higher levels in the fungi than in most 

 bacteria. Mycobacterium and related forms, however, are exceptions 

 to this rule and may have a rather high lipid content (130). 



35 



