42 THE COMPOSITION OF FUNGUS CELLS 



4. CELLULAR CARBOHYDRATES 



In this section are included polysaccharides and related compounds 

 exclusive of chitin, just discussed. Some of these may be found later 

 to be associated with the cell wall, and others appear in the medium 

 as well as the mycelium. Characteristically, cells grown on high-carbo- 

 hydrate media are rich in polysaccharides; for example, the mycelium 

 of Aspergillus niger may be 25 per cent polysaccharide (148). 



The first fungal polysaccharide to be studied was that of Penicillium 

 glaucum spores, named "spore starch" by Cramer (29). In the period 

 from 1894 to about 1925 several polysaccharides were described, but 

 with few exceptions the criteria of identification were inadequate and 

 the nature of the materials remains in doubt. These early studies have 

 been reviewed by Dox and Neidig (36) and by Schmidt (149). It need 

 only be pointed out here that none of the presumed identifications 

 with the starch of higher plants is based on sufficient evidence. 



Fungal polysaccharides of known or partially known constitution 

 are listed in Table 4. Most are formed by species of Penicillium and 

 Aspergillus, but this may only mirror the more intensive study which 

 has been devoted to these genera. The most common sugar com- 

 ponent is glucose, the next most common galactose. 



Galactocarolose is distinguished by two unusual features: galactose 

 is in the furanose form, and the galactose units are joined by a 1,5- 

 glycosidic bond (76). It has been speculated that the galactofuranose 

 structure may be metabolically related to the tetronic acid derivatives 

 also formed by Penicillium charlesii (Chapter 6). 



The glycogen of fungi is chemically identical with or very similar 

 to that of animals (40) and occurs also in yeast (118). The fraction 

 appearing as glycogen in routine analyses usually comprises about 5 

 per cent of the mycelial or spore dry weight (140, 171), but in the 

 sclerotia of Phymatotrichum omnivorum the glycogen content is 36.7 

 per cent (40). 



Polysaccharides of which the constitution is not fully known include 

 especially the hemicelluloses, defined by their solubility and ease of 

 hydrolysis. The crude hemicellulose fraction of Aspergillus niger 

 constitutes 12 to 31 per cent of the dry matter of the mycelium, and 

 is, like several other constituents of the mycelium, profoundly affected 

 by the supply of metals in the medium (129, 156). Pentosans have 

 been isolated as about 1 per cent of the dry matter of fungi (35, 150), 

 but the possibility that these materials are in fact hemicelluloses can- 



