They can resist desiccation by producing thick, melanized walls which are often seen in aerial spores, in hyphal strands, and in sclerotia that enable the fungus to survive suboptimal growing conditions in the soil for several years. The fungal wall usually consists of layers of chitin, a linear polysaccharide polymer of N-acetylglucosamine, embedded in and often cove ed by glucans, branched polymers of glucose and other sugars. Some species of fungi in the Class Oomycetes such as Phytophthora and Pythium have cellulose walls rather than chitin. The melanin components consist of branched polymers of phenolic material similar to the lignins of plant cell walls. Return to Top of Document 2.
Saprophytic fungi are the decomposers and live on dead organic material.
They play a major role in the re-cycling of nutrients. Decay by fungi is usually considered in a negative context as the rotting of wood products and textiles or the mold or mildew on paint or bathroom tiles. But, fungal decomposition is benefial as can be seen in the thermophilic composting process in the backyard or the barnyard. Think of the incredible build-up of organic leaf litter in the forest without the saprophytic activity of the fungi. As obligate or biotrophic parasites such as wheat rust, they must obtain nutrients from living cells.