NUTRITION 79 



roots becoming invested or even penetrated by them. These 

 associations, described by Frank* most fully, are still too 

 little understood to enable one to determine what parts are 

 played by the members, or to decide whether the associa- 

 tion is of mutual advantage or not. 



The association of filamentous fungi with the roots of 

 higher plants called Mycorhiza by Frank* is not confined 

 to those poor in chlorophyll (e. g. Neottia) or devoid of it 

 ( e. g. Monotropa ) , but occurs also in a considerable number 

 of green plants (e. g. many Orchidaceae, Ericaceae, Cupuli- 

 ferse, Piuus, etc.). This, coupled with the fact that so little 

 is known of the chemistry of nutrition in these associations, 

 renders it impossible to draw any general conclusions re- 

 garding the work accomplished by the fungi. Those closely 

 investing and making felt-like sheaths over the roots of 

 certain forest trees (e.g. beech and pine) cannot be sup- 

 posed to furnish the larger member of the association with 

 non-nitrogenous carbon compounds from the soil, for these 

 it can elaborate in abundance in its own green leaves. 

 Mineral salts and appropriate nitrogen compounds the fun- 

 gus may supply, first, because of its ability, by reason of 

 its smaller size, to branch more finely and spread more 

 widely among the soil-particles than can the roots ; second, 

 because of its decomposing action upon insoluble nitroge- 

 nous remains in the soil ; and third, because it may elaborate 

 or oxidize the otherwise useless ammonia compounds. f 



It is claimed that the fungi may be of additional ad- 

 vantage because roots invested by them branch more pro- 

 fusely than naked ones, and hence are intimately in contact 

 with more soil particles and have a larger absorbing sys- 

 tem. J Neither in this claim, nor in the observation that 

 root-hairs are largely absent from the roots of green as well 



* Frank, A. B. Lehrbuch der Botanik, Bd. I., 1892. Also Percy Groom 

 in Annals of Botany, Vol. 9, 1895. See also Stahl, E. Der Sinn der 

 Mycorhizenbildung. Jahrb. f. wiss. Bot., Bd. 34, 1900. MacDougal, D. 

 T. Symbiotic saprophytism. Annals of Bot., XIII., 1899. 



t Frank, A. B. Die Krankheiten der Pflanzen, 2te Aufl., 1895. Also 

 die Bedeutung der Mycorhiza-Pilze fiir die gemeine Kiefer. Forstwissen- 

 schaftliches Centralblatt, XVI., 1894. 



t Stahl, E. Loc. cit. 



