Kelley — 12 — Mycotrophy 



forest trees is largely conjectural. From information now extant 

 one cannot say with accuracy whether trees have root-hairs or mycor- 

 rhizae, much less the exact mode of nutrition of any particular kind 

 of tree. Even were it concluded that the tree was nourished with 

 the aid of mycorrhizae, the precise nature of mycotrophism is still 

 in doubt. Hence the foresters' dealings with trees are akin to the 

 mediaeval doctor's treatment of his patients. 



Ecology of Mycorrhizae*: — The earlier mycotrophic problems 

 in ecology involved the relation of mycorrhizae to sandy soils and 

 to humus. More recently there has been discussion regarding the 

 presence or absence of mycorrhizae in prairie soils with reference 

 to establishment of trees on such areas. It has been claimed that the 

 endophytes are absent from prairie soils and that such soils must be 

 inoculated with suitable fungi before mycorrhizae will be formed. 

 But investigators have not been careful to distinguish between prairie 

 soils and the more arid steppe soils. Then, too, several investigators 

 report abundant endophytes in these soils, and recent observations 

 show that there is a rapid spread of trees into certain prairie areas. 



As to soil reaction, there is more nearly an unanimity of opinion, 

 for it is evident that mycorrhizal fungi thrive best in acid media. 

 Hence, mycotrophic structures are more likely to be found in acid 

 soils while root-hairs may be expected in mull soils. But in regard 

 to soil solution, little can be said, for in spite of the number of in- 

 vestigations into nutritional and soil problems and the multiplicity of 

 papers on salts in soil solution, the actual connection of the plant 

 with the soil has been almost completely ignored. To say that a plant 

 has mycorrhizae and is nourished by mycotrophy has been regarded 

 as sufficient, and whether materials get from the soil into the plant 

 by mechanical means or by black magic is left to the imagination of 

 the reader. All the detailed studies of soil solution in the B horizon 

 have no necessary connection with a large proportion of plants in 

 native habitats. And thus the mechanism for the intake of materials 

 into mycorrhizae is a subject of research awaiting investigation. Yet 

 some attention has been paid to the microhabitat of the fungus-root 

 and its community of organisms, the rhizosphere as it has been appro- 

 priately called. 



*A valuable paper on the ecology of ectotrophic mycorrhizae, by Dr. J. L. 

 Harley, of Oxford, has recently appeared in Biological Reviews. 



