134 PHYSIOLOGY OF THE FUNGI 



more monosaccharides or related compounds on hj^drolysis. Cellulose, 

 starch, and glycogen are members of the first class and yield glucose on 

 hydrolysis. Polysaccharides are frequently named b}^ replacing the end- 

 ing -ose of the parent monosaccharide by -an. Fructan (le\ailan) desig- 

 nates a polysaccharide which yields fructose on hydrolysis. A hexosan 

 is a polysaccharide which yields hexose sugars on hydrolysis, and a pen- 

 tosan yields pentoses. Pectins are polymers of galacturonic acid. 



The heteropolysaccharides occur in lesser amounts than the homopoly- 

 saccharides. Among them are the hemicelluloses, which on hydrolysis 

 yield D-xylose as the principal sugar, the plant gums, and agar. 



Cellulose. Chemically, cellulose is a linear polymer of o-glucose. The 

 glucose residues are joined together through /3-glycoside linkages as in 

 cellobiose, and cellulose may be thought of as consisting of repeating 

 cellobiose units. Norman and Fuller (1942) postulate that the majority 

 of fungi are able to utilize cellulose. In spite of the importance of cellu- 

 lose utilization by fungi in the economy of nature much remains to be 

 learned about this process. 



It is commonly accepted that the first stage in utilization of cellulose is 

 hydrolysis, although Campbell (1932) has suggested oxidation. The 

 hydrolysis of cellulose may be expressed schematically as follows: cellu- 

 lose — > cellodextrins -^ cellotetrose -^ cellobiose -^ D-glucose. Fungus 

 cellulases appear to have been infrequently studied. Grassmann et al. 

 (1933) separated cellulase and cellobiase from Aspergillus oryzae. This 

 cellulase was inactive in hydrolyzing cellulose degradation products hav- 

 ing a molecular weight less than 1,000 (six glucose residues), while the 

 cellobiase hydrolyzed cellulose fragments containing from two to six 

 glucose residues. 



Fungi differ widely in ability to utilize cellulose. In general, the rate of 

 utilization of cellulose is less than that of glucose. This is probabty due 

 to the insolubility of cellulose, which limits the action of cellulase to the 

 surface, or to an inadequate rate of enzyme synthesis. 



The principal source of cellulose available to fungi in nature is wood and 

 other plant remains, ^^^lile cellulose is the chief constituent in such 

 materials, hemicelluloses, gums, tannins, and lignin are also present. 

 The wood-rotting fungi have been classified according to whether they 

 cause white or brown rots. The fungi which cause brown rots attack 

 cellulose in preference to lignin. The fungi which preferentially attack 

 the noncellulosic constituents of wood cause white rots. The latter 

 species are apparently more numerous than those which cause brown rots. 

 The following are some of the fungi listed by Nobles (1948) as causing 

 white rots: Armillaria mellea, Ganoderma lobaturn, Lenzites hetulinus, 

 Pleurotus ostreatus, Polyporus ahietinus, P. cinnabarinus, P. pargamenus. 

 A few fungi causing bro^^^l rots are Daedalea quercina, Lentinus lepideus, 



