Kelley — 154 — Mycotrophy 



mycotrophs apparently make use of organic N compounds through aid 

 of their mycorrhizae, this action taking place best on acid soils, the 

 occurrence of mycotrophs on alkaline soils therefore becoming 

 impossible. 



Weyland (1912) initiated micro-chemical studies of the occur- 

 rence of salts in tissues of mycotrophic plants, and concluded from 

 his studies that, as a result of a limited transpiration stream which 

 results in part from activity of the fungus, P and K would be de- 

 veloped in concentrated form in the plants. The plants could thus 

 satisfy their Ca-requirement only by living on a calcareous soil from 

 which they evidently take the Ca. The theory of winning nutrient 

 salts through fungal aid, which the author (Weyland) had learned 

 from his teacher, Stahl^ broke down at this point. Nitrogen (Harn- 

 stoff) in orchid tubers was regarded as a metabolic product of the 

 root fungi. N-assimilation is to be considered as an essential func- 

 tion of the root-fungus. 



An extended micro-chemical study of mycorrhizae was made by 

 Rexhausen (1920) who, seeking particularly to test Weyland's 

 conclusions, found that mycorrhizae were as rich in P and Ca as 

 were the fungus-free roots; also in protein content, although it 

 seemed somewhat greater in infected plants. He said that mycor- 

 rhizae are to be seen as isosmotically acting individuals which provide 

 the plants with all nutrient salts, apparently not merely P and Ca. 

 He thought that the fungus takes N from the higher plant because 

 of the ease of acting as a parasite in comparison with difficulty of se- 

 curing nutrient salts from the humus. Only in soils rich in nutrient 

 for the fungus can the higher plant throw off the fungus. But he 

 was sure of the nutrient salt provision for he repeats: "In the other 

 plants studied it may be stated positively that nutrient salts are brought 

 into the root through the hyphae." 



Finn (1942) found in culture studies of white pine that seedlings 

 provided with mycorrhizae took in more N and K per seedling than 

 those of uninoculated controls. Earlier, Mitchell, Finn & Rosen- 

 DAHL (1937) had reported that their observations "indicate that the 

 benefits attributable to mycorrhizae, like their distribution in nature, 

 vary inversely as the concentration of readily available mineral nu- 

 trients in the soil. Seedlings lacking mycorrhizae are unable to exist 

 in very infertile substrates." 



Importance of P: — In some cases at least, P seems of greater im- 

 portance than N. Thus McComb (1943) states that with pines, 

 especially P. Banksiana, good growth followed P fertilisation while 

 little or no response was obtained with N. "Without mycorrhizae 



