Kelley — 78 — Mycotrophy 



soil. The soil is merely an anchorage medium for the higher plant 

 and the fungus is its body servant that makes contact with the soil. 

 It is the fungus that benefits from acid reaction and is limited in its 

 pH range. Modess (1941), in his investigations of mycorrhizal 

 fungi, found that all investigated fungi produced acid solutions. 

 Optimum grovi^th occurred with the Amanita spp. at the pH range of 

 3.5-4.5 ; with Paxillus Primuhis and the Boletus spp. (with the excep- 

 tion of B. variegatus) at pH 5.0 or somewha loove this value, relative 

 to Lactarius delicosus and Rhizopogon roseolus at pYi 5.5-6.0. A 

 species of Mortierella isolated from Empetrum made best growth at 

 pB. 2.77-4.0 (Hasselbaum, 1931). 



It may be observed, however, that Henry (1936) records five 

 ectotrophs growing in Utah above the aspen zone where soil is neutral 

 or slightly acid; and Auret (1930) found the mycothalli of Lnnu- 

 laria growing in slightly alkaline soil of South Africa. Ridler (1923) 

 also reports Pellia in England on soils of pH 6.8-7.0. 



The Use of Free Nitrogen: — The several studies relative to 

 fixation of atmospheric N by mycorrhizae may be summarized by stat- 

 ing that if such fixation occurs it is in too small amounts to be of 

 consequence to the mycorrhizal plant. Melin (1922) found that 

 fungi associated with mycorrhizae of Pinus sylvestris and Picea Abies 

 can in no case fix atmospheric N ; and in 1925 he stated that there is 

 no fixation of free N in mycorrhizae of trees examined. Moller 

 (1906) had found that dichotomons mycorrhizae of Pinus montana 

 are of no use to the tree in fixing free N ; the fungus of Empetrum is 

 likewise unable to use atmospheric N (Hasselbaum, 1931) ; the same 

 is true of the fungus of Monotropa (Francke, 1934) ; and also of 

 Mycelium radicis Fagi A (Aali, 1923). But Rayner (1922a) claimed 

 that certain strains of Phoma isolated from ericaceous plants can use 

 atmospheric N and she said that Aspergillus and Penicillium are 

 similarly capable but in varying degrees. She backed Ternetz (1907) 

 who had published similar statements. Furthermore, Neilson-Jones 

 (1928), experimenting with a fungus isolated from Calluna, decided 

 that the "plant can obtain nitrogenous supplies from the air, probably 

 in the form of molecular N, in sufficient amount to prevent the advent 

 of any symptoms of N starvation." The volumes of culture solution 

 tested were 50-100 cc, and the amounts of N fixed, from 0.00004- 

 0.00384 gm. But Addoms (1931) decided that if atmospheric N were 

 fixed by Phoma radicis isolated from cranberry (Oxycoccus) plants, 

 it was in amounts too small to be of service to the higher plant. 



As to composition of the soil air in general and its effect on mycor- 

 rhizae, the author knows of no studies except that Laing (1923) 



