Kclley —158— Mycotrophy 



acquaintance with this hypothesis is through Romell's (1944) review, 

 from which the following is quoted: "the mycorrhizae seek soluble 

 carbohydrates in the root, and they consume them for energy, but 

 they find them only if there is a surplus of carbohydrate in the root. 

 Whether or not there is any surplus depends on the head-start photo- 

 synthesis (carbohydrate formation) has attained in the plant before 

 the formation of albuminous substances. This advantage will be 

 small or nil if there is an abundance of all plant foods including 

 nitrogen and phosphorus, so that there will not need to be a shortage 

 of materials when albuminous substances are built up. Then there 

 will be little for the fungi to seek after in the root, and mycorrhizae 

 will be formed sparingly or not at all. On the other hand, should 

 there be a deficiency of nitrogen or phosphorus foods, there can 

 easily arise a surplus of carbohydrates so that the formation of al- 

 buminous substances falls behind photosynthesis. With a moderate 

 lack of nitrogen or phosphorus or both, mycorrhizae can form 

 abundantly, but if there is a serious lack of nitrogen or phosphorus, 

 sooner or later photosynthesis will become weak also (phosphorus 

 especially strongly influences carbohydrate formation in plants) so 

 that the surplus of assimilated carbohydrate becomes less for that 

 reason, and mycorrhizae are formed more rarely. Similar reactions 

 occur if light becomes weak, Mycorrhisal formation is, expressed 

 briefly, a result of and a sign that there is a certain surplus of energy- 

 giving nourishment in the host plant." 



Carbonaceous Theories: — Besides the theories of mycotrophy 



which posit the intake of inorganic salts, there are not lacking 



theories that connect it with carbon. The idea that roots take in carbon 



has been familiar from the days of Liebig and his "humus theory" 



which posited a normal intake of carbonic acid by rootlets of seedling 



plants. The same idea appears in a paper by Breal (1894) who, in an 



experimental study concerned chiefly with cereals, concluded that 



these plants are able in efifect to take up organic carbon materials 



through their roots. Beauverie (1902) studied the Hverwort, Cono- 



cephalus, and found that endophytic infection is most pronounced 



where humus is most abundant, and where humus is lacking there is no 



mycelium and thallus is small sized. By experiment it was indicated 



that the plant secures part of its C from the humus. For the orchid 



Gastrodia, McLuckie (1923) came to the same conclusion: "Gastro- 



dia is an elaborate example of symbiosis in which an Angiosperm is 



associated with a fungus and a bacterium ; and is directly or indirectly 



dependent upon its endophytes for its carbonaceous and nitrogenous 



foods." Other examples are given by Young (1940). 



