FUNCTION OF MYCORRHIZAE 301 



component, in lieu of root hairs, functions to absorb water and 

 mineral salts from the soil. Some of Frank's experiments involved 

 growing seedlings in culture solutions free from mycorrhizae. He 

 found that such trees made entirely satisfactory growth, a result 

 that has been repeatedly verified by others. Frank's interpreta- 

 tions immediately created a great deal of interest throughout 

 Europe, and from the investigations that were undertaken in the 

 next few years a barrage of criticism arose. The net result of 

 these studies was the general admission that mycorrhizae are of 

 widespread occurrence in nature, but many workers questioned 

 the mycotrophic relationship. 



Stahl's comprehensive study (1900) of mycorrhizae is a land- 

 mark among contributions to the literature of this subject. In it 

 he elaborated the thesis that the incidence of mycorrhizal devel- 

 opment is correlated inversely with soil fertility. Supporting 

 evidence for this thesis rests in part upon the assumption, since 

 confirmed by a host of investigators, that in the keen competition 

 between vascular plants and soil fungi for essential minerals, the 

 fungus mycelium possesses superior mechanism. Presumably the 

 basis for this superiority is that the ratio of surface area to volume 

 is vastly greater in fungus hyphae than in roots. For this reason 

 non-mycorrhizal plants, such as Sambiicus nigra, Cvperaceae, and 

 various ferns, are at a disadvantage when growing on infertile soils, 

 in competition with mycorrhiza-formers. 



Stahl's observations also bore out his assumption that different 

 species of plants differ in the extensiveness of their root systems 

 and their rates of transpiration. Species with extensive root sys- 

 tems and with the capability of losing water rapidly might be 

 expected to be best fitted for competition. Actually Stahl found 

 that the reverse is true, for the reason that species possessing ex- 

 tensive root systems and being capable of transpiring rapidly tend 

 to be autotrophic, whereas those with restricted root systems and 

 slow transpiration rates are mycotrophic. 



Rayner (1934) concluded from researches involving pines that 

 there is a "direct causal relation between mvcorrhiza development 

 and the thrifty growth in seedlings of various species of Pinus." 

 Further evidence in support of Stahl's mineral-nutrition theory is 

 advanced by Hatch (1937) in an extensive series of experiments. 

 He emphasizes that the absorbing surface area of short roots is 

 increased through the presence of mycorrhizae by the following: 



