Kelley — 150 — Mycotrophy 



deriving no benefit from the fungus in its roots." But MacDougal 

 & DuFRENOY (1944) say that "The non-necessity of the fungus for 

 germination of terrestrial orchids has been wrongly taken as a proof 

 of parasitism by J. F. Curtis." 



A similar comment could be made of Renner's (1935) assertion 

 that because seeds of Salix and Acer germinate without fungal aid, 

 also because soil-grown plants grew equally well without fungi while 

 weaker plants in water-culture were killed by the fungi, that the 

 symbiosis is a tolerated parasitism. 



Magrou (1921) took the position that mycorrhizal symbiosis is 

 on the border of disease. In perennial plants, as the potato, the fungus 

 is in part phagocytized while in annual plants (as Orobus) it was 

 completely destroyed. Limitation of the fungus was thought due to 

 toxic constituents of the cell-sap, while tubers appear as symptoms 

 of disease. In 1928, Magrou inclined to the view that the fungi are 

 mdififerent parasites which, if not harmful in all cases, are without any 

 use. 



Schools of Mycotrophism: — Those who reject the parasitic 

 view of the mycorrhizal symbiosis and believe in mycotrophism are 

 divided amongst themselves into several divergent schools of thought. 

 They all agree that the mycorrhizal fungi are useful to the higher 

 plant, but they disagree as to what the mycorrhizal fungi afford to 

 the higher symbiont. 



Mycorrhiza Replaces Root-Hairs: — One of the earliest views 

 was that the mycorrhizal fungi, through the hyphae that connect 

 mycorrhiza with soil, take the place of root-hairs and provide thS 

 higher plant with nutrient. Pfeffer (1877) said that in rhizome and 

 roots of saprophytic orchids there frequently appears a fungus the 

 mycelium of which, at least in Neottia, is found in living cells and 

 sends out strands to the outside which, like root-hairs, take up 

 organic and inorganic soil portions and with them make growth. Per- 

 haps Pfeffer borrowed the idea from Drude (1873) who had said: 

 "This constant entrance of a parasite into definite layers of the sub- 

 terranean organs requires closer consideration. We have never found 

 it in the epidermis : the question arises whether the basis thereof is 

 not to be sought in the circumstances connected with the nutrition, 

 whether perhaps the mycelial threads in these cell layers might not 

 yield a rich nutrient." Marcuse (1902), after a study of representa- 

 tive mycorrhizae of a number of plants, came to the conclusion that 

 "in most endotrophic mycorrhizae the communication-hyphae have a 

 physiological role comparable to root-hairs, as was first hypothesized 



