Lecture I — 7 — Rise of Mycotrophy 



study for he turned to other studies, but he returned to the defence 

 of his hypothesis of mycotrophy from time to time. At first he 

 thought that mycorrhizal fungi are concerned especially with nitrogen 

 nutrition of the higher plant, bringing nitrogen salts into the 

 mycorrhiza. But later he taught that the higher plant is actually a 

 parasite on the fungus, drawing it into the root, tending and finally 

 devouring it. 



Bernard and Orchid Symbiosis: — At the turn of the century 

 a new phase of mycotrophic study was developed. Hitherto the 

 interest had been chiefly with forest plants, following the initiative 

 of Frank. But when Noel Bernard began to publish on myco- 

 trophism of orchids an important new branch of science was opened 

 up. Bernard isolated from orchid tubers fungi which he classified 

 into three groups and placed in the genus Rhizoctonia. These fungi, 

 he found, were able to cause orchid seed germination and, lacking 

 presence of a fungus, there was no germination. It is interesting 

 to note that Salisbury, when he described orchid seed germination 

 in 1804, failed to note presence of fungus. But Bernard did not 

 assert that a fungal symbiosis was an inevitable necessity, for he 

 induced asymbiotic germination of orchid seed with salep, a poly- 

 saccharide derived from dried orchid tubers. Sterile cultures were 

 grown by Knudson, who showed that in greenhouse propagation 

 of orchids sugars may be used in germination of the seeds in place 

 of fungi ; but in nature it is of course the fungus that is responsible 

 for the germination. 



Even before Bernard's untimely death m 1911, Burgeff had 

 been publishing on orchid mycotrophism. He called the endophytes 

 Orcheomyces, but later made use of the less convenient designation 

 of Mycelium radicis. 



Tuber Formation and Perennism: — Bernard was convinced 

 that tuber formation in orchids and other plants was due to their 

 symbiotic life with fungi, and that after many generations of such 

 symbiotic life the "habit" of forming tubers was acquired so that 

 tubers were still formed by the plant even in the absence of fungal 

 aid. Thus the potato, native of Andean highlands, formed tubers in 

 the Andes in symbiosis with a species of Phoma, but in northern 

 latitudes, as in France, tubers were still formed without presence 

 of a fungus. He advanced the idea that influence of a cold climate 

 parallels the action of the fungus, and pointed out that in a hot 

 climate such as that of Algiers, tuber formation "degenerated" and 

 tubers were no longer formed in absence of a fungus. Using this 



