Relley — 80 — Mycotrophy 



a sterile one. Greaves & Jones (1944) have suggested that addition 

 of manure to soil may add new microorganisms and modify the soil 

 temperature. 



Altitude: — The production of mycorrhizae at various altitudes 

 has been studied especially by Costantin and his associates, the effect 

 of altitude being considered due to air temperature and thus parallel- 

 ing effect of latitude. In 1926 Costantin & Magrou observed 

 similarity of mycorrhizae of Dryas octopetala in the Alps and in the 

 arctic as described by Hesselman. Hitherto only ectotrophic mycor- 

 rhizae had been observed in such situations but now endotrophic my- 

 corrhizae were found widely distributed in the Alps. Annual plants 

 are absent from the Arctic and rare in the Alps, but the annual 

 Gentiana campestris was found to have an endophyte which, however, 

 underwent a "brutal phagocytosis". The authors came to an important 

 tentative conclusion that if essentially mountain genera are found 

 sporadically on the plain, their stations rest ephemerally because the 

 mycelium which is transported accidentally at the same time as the 

 seed does not reproduce itself. Later (1934) these same investiga- 

 tors, with associates, grew potato seed at 1,400 m.A.T. and obtained 

 some plants with infection, some without; but at 550 m.A.T. all the 

 plants died without producing a tuber. Since potatoes are not ordi- 

 narily grown in these alpine places, the authors concluded that potato 

 can form mycorrhizae with fungi already present in such situations. 

 These results are aligned with the theory that the mycorrhizal habit 

 in alpine plants commenced with a chance association of fungus and 

 root, forced beneath ground by inclement weather. Whatever value 

 this theory may have, it seems better established that there is an 

 optimum altitude for mycotrophy. Bouget had studied potato since 

 1901, and in 1922, with Bonnier, discovered the law of optimum 

 altitude, which was not published until rediscovered and published by 

 Lebard in 1931 (Costantin, 1936). Lebard & Magrou (1935) 

 state that, through three seasons' experiments it was shown that there 

 is an altitude where yield of potato is maximum, decreasing above or 

 below. 



Light: — Light can affect mycorrhizae only indirectly since they 

 are not ordinarily exposed out of the soil. But illumination does affect 

 the vigour of the host plant, and the production of ionizable substance 

 in the host tissues. Bjorkman {cf. Romell, 1944) has studied the 

 effect of light on seedlings and it is stated that mycorrhizae are formed 

 in weak light (1/16 or sometimes 1/8 full sunlight), but under 

 greater illumination there were better seedlings with more mycor- 



