Kelley — 178 — Mycotrophy 



organs (being fungus-free) are full of starch, which occurs nowhere 

 else. In Lycopodium, infected cells contain oil rather than starch 

 (Bruchmann, 1906), while in Pellia (Ridler, 1922) the fungus 

 uses starch "which is replaced by oil after entrance of fungus". Again, 

 in higher plants it is found that "Whereas in non-infested roots the 

 starch is deposited indiscriminately, in those colonized by mycorrhizae 

 it preponderates in the cells free from mycelium" (Endrigkeit, 

 1937). Added evidence that carbohydrates are used by the fungus 

 is provided by Bjorkman (1944) whose experiments show that 

 pine on being "strangled" by a wire placed 5 cm. above the ground 

 level formed almost no mycorrhizae while the amount of soluble car- 

 bohydrate in the roots dwindled. Bjorkmann believed that mycor- 

 rhizal form is largely conditioned by an excess of soluble carbohy- 

 drate in the roots. The fungus can use only a readily soluble carbo- 

 hydrate like glucose, as shown by Melin & Norrkrans (1942). 

 Magrou has found that formation of potato tubers is conditioned by 

 the osmotic pressure of sugar within the cell. In nature, it is the 

 mycorrhizal fungus which ordinarily changes starch of the plant cell 

 into sugar. "Ce processus de dislocation des parties colloidales du 

 protoplasme a ete designe par Errera sous le nom d'anatomose" 

 (Ann. d. Sci. nat. Bot., XI, 4:97-102, 1943). 



Rexhausen (1920) has summed up the matter by saying that 

 the fungus takes carbohydrates from the plant in the form of sugar. 

 Thus sugar is obviously obtained by use of the plant's reserve starch. 

 Or, as MacDougal & Dufrenoy (1944) state : "Hydrolyzation prod- 

 ucts of polyuronides, of starch, and of other dififusible compounds 

 may be absorbed by the fungus." 



At the same time Young's (1940) objection must be taken into 

 account : "The concept of the higher plant obtaining carbohydrate 

 from its fungus symbiont is in direct contradiction to the unsupported 

 but generally assumed theory that the mycorrhizal fungi obtain carbo- 

 hydrate from the tree roots as their share of the symbiotic relation- 

 ship. The hymenomycetous fungi which form the mycorrhizas are, 

 however, quite capable of obtaining their own carbohydrate supply 

 from the breakdown of organic matter. This is evidenced by their 

 vigorous growth on raw organic substrata and is supported by the ex- 

 perimentally proved fact that one of the major functions of the fungi 

 associated with orchid roots is to supply carbohydrate to the higher 

 plant." The solution of this problem would seem to lie in this, that the 

 fungus "dissolves" starch as it invades the tissues of the higher plant, 

 and releases later to the higher plant whatever it has brought from the 

 soil on phagocytosis. The action would seem to be in both cases 

 mechanical. 



