Most species of Trichoderma and Gliocladium are saprophytes, and their respective teleomorphs are lignicolous ascomycetes (see Volume 1, Chapter 5). Hence, they encounter in nature a wide variety of polymeric substrates among which celluloses and hemicelluloses predominate. Cellulose chains are j?-1,4-glucosidically-linked homopolymers of about 8000-12000 glucose units, which are held together by hydrogen bonding to form essentially insoluble crystalline cellulose. Hemicellulose is a general term summarizing various heteropolysaccharides which are based on backbone polymers formed of xylose (xylans) or mannose (and glucose) (mannans, glucomannans) and which have additional side-chain substituents such as arabinose and galactose, and acetic and glucuronic acids (see Chapter 2). Pectins are even more complicated with various branched structures. In contrast to degradation of cellulose, which leads to glucose and glucooligomers, degradation of hemicelluloses leads to the accumulation of various mono-and disaccharides in various ratios depending on the hemicellulose type. Other polymers such as j?-glucans, starch and protein account only for a smaller part of available carbon, although they may predominate in certain habitats (Chapter 6).