Kelley — 142 — Mycotrophy 



Necessity of Orchid Fungus: — Here was a thesis around which 

 a battle was waged. Bernard continued to develop his idea (1903) : 

 An orchid seed germinated aseptically, he said, will swell to a large 

 diameter but will then still be stationary after 100 hours of culture, 

 but transported to a pure culture of the hyphomycete will germinate 

 at once. "This case is, I think, the first certain example of an organism 

 which is not normally able to get past an erabyronic state without 

 penetration of a parasite, just as an egg, e.g., cannot pursue its de- 

 velopment without fertilisation. Using a term which has been applied 

 to lichens, we may say that we have made the synthesis of a plantlet 

 of the orchid." These plantlets are not comparable to those of the 

 majority of plants, which are derived from an egg, but are complex 

 forms of the value of mycocecidia {i.e., mycodomatia). Bernard 

 (1904) proceeded to isolate the orchid fungi, finding a number of 

 which some induced germination and others not. In 1905 he recorded 

 experiments showing orchids exceptionally difficult to germinate de- 

 pend on endophytes different from those already isolated from 

 Cattlyea and Cypripediiim : thus there is a differential power amongst 

 the fungi. He said (1909a) : RJiizoctonia repens affects the majority 

 of orchids but R. languinosa and R. mucoroides infect them with 

 comparative rarity. (The orchid fungi are generally basidiomycetes : 

 cf. Derx, 1937; Sprau, 1937). 



Degeneration of Orchid Fungus: — Then came a statement that 

 added a fresh discussion : The activity of each species of fungus is 

 not fixed but dwindles rapidly when the Rhizoctoneae live apart 

 from the orchids : it does not require more than 2-3 years to cause 

 their activity to become unappreciable. Burgeff (1909), recounting 

 his own experiments, stated, however, that while Bernard found that 

 orchid fungi, which are essential to germination of the seed, soon 

 lose their virulence if cultivated for some time apart from the orchid, 

 he himself found that the fungus of Hahenaria psychodes and others, 

 in spite of over 2 years culture on starch-agar exhibited the same 

 infection-power which the fungus had earlier possessed. He felt 

 that any idea of a decadence in infective power of the fungus should 

 be abandoned. (It may be noted here that Wolff, 1923, found that 

 the age of orchid seed determines its power of germination, 

 vitality dwindling rapidly after maturity and at the end of 38 months 

 there was no germination.) Burgeff isolated a considerable number 

 of orchid fungi which he at first termed Orcheomyces but later 

 called Mycelium radicis. That it is the orchid root fungi that cause 

 germination of orchid seed was further demonstrated by Sprau 

 (1937), who isolated a Rhizoctonia from Orchis masculus that stimu- 



