POLYSACCHARIDES 77 



in wood (85, 169) and in other plant materials (143, 179); the extensive 

 early literature on hemicellulose breakdown in soil is reviewed by 

 Waksman and Diehm (225). 



Purified pentosans are attacked by most fungi and actinomycetes 

 which have been tested (80, 99, 124, 216, 225). 



Cellulose. Cellulose, the principal structural polysaccharide of 

 plants, is by far the largest reservoir of biologically utilizable carbon 

 on the surface of the earth, and its decomposition, in which fungi 

 probably play a major role, is of great ecological importance. Struc- 

 turally, it is a linear polymer of D-glucose, the configuration being that 

 of a l,4-/?-glucoside. The number of units in the polymer is high; 

 probably individual linear chains are connected by cross-linkages. 

 Complete hydrolysis yields glucose, partial hydrolysis the disaccharide 

 cellobiose. 



The literature on the utilization of cellulose by fungi is very large, 

 beginning with the observations of the pioneer plant pathologists of 

 the nineteenth century. Unfortunately, frequent reliance on inade- 

 quate criteria makes it difficult to evaluate this work, and much of it 

 must be considered of doubtful validity. The early literature is re- 

 viewed by McBeth and Scales (123), Otto (147), and Waksman (223). 

 The monograph of Siu (186), especially concerned with fabric deteri- 

 oration, offers the most complete survey available of more recent work. 



Several methods have been used in attempts to assay the ability of 

 fungi to grow on or destroy cellulose. Some of these, e.g., observation 

 of the erosion of cotton fibers (56, 147) and measurement of the loss 

 in breaking strength of rotted cotton fabric (73, 214), are adequate for 

 their purpose but do not measure growth directly. Similarly, measure- 

 ment of gas exchange during growth on cellulose (55, 107) determines 

 an activity which is not necessarily a function of growth. 



Visual estimate of growth on filter paper or other cellulosic materials 

 is by itself of no value as an index of growth or cellulolytic capacity 

 (126). Growth on reprecipitated cellulose in agar (123) is equally un- 

 reliable, probably because of chemical changes occurring in the prep- 

 aration of the cellulose (143). 



The quantitative methods which seem most promising are the fol- 

 lowing: 



1. Measurement of growth on or hydrolysis of carboxymethylcellu- 

 lose, a soluble cellulose derivative (96). However, the correlation of 

 this property with cellulolytic capacity is uncertain (163). 



2. Chemical determination of the disappearance of cellulose from 

 complex natural materials. This has been applied extensively, to 



