Lecture XI — 149 — Theories 



A number of investigators have concluded that the endophytic 

 relation is a parasitism after experimental study. Thus, F. Fuchs 

 (1911), who originated synthetic experiment in mycorrhizal study, 

 came to the conclusion after studying synthetic mycorrhizae of coni- 

 fers, that there is no symbiosis here of the sort in which the host 

 plant is benefited. Where fungal hyphae penetrated into cells they 

 were deformed and killed while the infested cells turned brown and 

 were thrown off by the root. This holds good for endotrophic roots 

 as well. The wide distribution of mycorrhizae indicates that it is 

 an endured parasitism (ertragbares Parasitismus) in which the host 

 plant suffers no injury because it is able to render the fungus harm- 

 less. With our present knowledge we can see that Fuchs was partly 

 right and partly wrong. 



H. Gordon (1937) was led to the view that the endophyte of 

 Rhododendron spp. is a relatively feeble parasite and of no specific 

 importance to the higher plant by the observation that in culture the 

 higher plant can form roots and establish itself in the total absence of 

 any micro-organisms. Needless to point out, Gordon worked only 

 under the highly artificial conditions of culture and did not deal with 

 actual plants in nature. Christoph (1921), like Gordon, concluded 

 in the case of other ericads, that the fungus is simply a harmless para- 

 site that does not injure the plant, because he was able to raise sterile 

 plants in culture, and in nature he says that Erica, Calhina, the Pyrolas 

 and Monotropae are only facultatively mycotrophic. 



Curbed Pathogens: — Similar opinions are expressed regarding 

 orchids. Bernard himself was no mycotrophist, but regarded the 

 endophytes as invaders that are checked by an humoral substance in a 

 phagocytosis that immunizes the remaining tissues of the plant. 

 CosTANTiN (1926) confirms Bernard and regards the orchids as 

 pathological, being hereditarily accommodated to their disease. It was 

 perhaps with such precedents in mind that Burges (1936) wrote: 

 "The presence of a fungus in a mycorrhizal association is to be 

 regarded as an example of controlled parasitic attack and has no 

 mutualistic significance. The fungi are weak pathogens whose activity 

 is curbed by the reactions of the host-cells. . . . One seems justified 

 in concluding that the mycorrhizal fungi, both ectophytic and endo- 

 phytic, are potential parasites controlled by reactions of the host- 

 cells." Curtis (1939) likewise votes for parasitism, influenced by 

 a cultural study of possible specificity amongst orchid fungi. From 

 the fact that orchid seed can be germinated asymbiotically and that 

 the orchid-fungus relation is non-specific, Curtis concluded "that 

 the symbiotic relationship is one of parasite and host, with the orchid 



