CONCLUSION 91 



It may be that the appropriate theoretical framework for carbon 

 nutrition is more the ecology than the phylogeny of fungi. The char- 

 acteristics of the phycomycetes outlined above can be understood as 

 related to the aquatic habit of most of the forms so far studied just 

 as easily as they can be interpreted in terms of taxonomy or phylogeny. 

 The carbon nutrition of the mycorrhizal basidiomycetes is another 

 example. The evidence is incomplete and not entirely satisfactory, 

 but it appears that this group is restricted in its carbon nutrition to 

 simple sugars, starch, and the pectic substances (74, 91, 130, 131, 170). 

 These fungi stand, therefore, in contrast to the litter-decomposing and 

 wood-rotting basidiomycetes, which use cellulose, lignin, or both. At 

 least one mycorrhizal basidiomycete, however, does form an adaptive 

 cellulase (142). 



The order Mucorales is cited often as a group of "sugar fungi" un- 

 able to utilize cellulose (26). This characterization appears to be 

 sound, although relatively few of the Mucorales have been adequately 

 investigated. Ecologically, however, the "sugar fungi" include a num- 

 ber of the Fungi Imperfecti, especially species of Aspergillus and 

 Penicillium, found in soils high in fresh organic matter and in carbo- 

 hydrate-containing materials. The line between "sugar fungi" and 

 cellulose-utilizing fungi cuts therefore across taxonomic boundaries, 

 since different species of Aspergillus, for example, are found in one 

 or the other group. 



In Table 1 are collected some data on the carbon nutrition of 

 different fungi, although it cannot be said that the organisms chosen 

 are in any way typical. The organisms of wide substrate range in- 

 clude a large group of soil saprophytes and plant parasites — Asper- 

 gillus oryzae, Brevilegnia gracilis, Fusarium oxysporum f. riicotianae, 

 Memnoniella echinata, Penicillium digitatum, Phytophthora cacto- 

 rum, Psalliota bispora, Stachybotrys atra, and Streptomyces coelicolor. 

 In comparison, the aquatic phycomycetes in the list appear more 

 fastidious; the contrast between the soil-inhabiting Brevilegnia gracilis 

 and the closely related aquatic Saprolegnia delica is particularly in- 

 structive. On the other hand, the plant parasite Chalara quercina has 

 a much narrower nutritional range than the aquatic Pythiogeton sp. 

 The most restricted of all in the group are Entomophthora coronata, 

 parasitic on insects, and the aquatic Polychytrium aggregation. 



The fungi parasitic on animals might be expected, by analogy to 

 bacterial parasites, to be nutritionally specialized. The available data 

 indicate that these fungi are not in fact particularly fastidious with 

 respect to carbon sources (140, 200). 



One incidental problem may be mentioned here. Throughout this 



