Lecture III 



THE FUNGAL ENDOPHYTES 



Nature of the Mycorrhizal Fungi: — It scarcely needs to be 

 said that mycorrhizal fungi are not a separate taxonomic unit in the 

 classification of fungi. They are the ordinary soil fungi of forest 

 and woodland, of meadow and cultivated field. Neither are they 

 special members amongst the congeries of soil fungi in the sense that 

 one, and only one, member can achieve a mycorrhiza. One fungus or 

 another can produce it, and ordinarily there may be several fungi par- 

 ticipating, forming what has been called a "multiple mycorrhiza". In 

 other words, the fungi living in the soil grow into plant roots as into 

 a part of their environment, and, if the host plant is able to check the 

 fungus in its rootlet cortex and break down the fungal hyphae, the 

 association is said to be mycorrhizal. Presence of the fungus, re- 

 gardless of its taxonomic identity, has little to do with the form of 

 the mycorrhiza, which is characteristic for a given host plant and is 

 determined by the host. In an informing paper by Magrou, Douchez 

 & Segretain (1943), it is shown that mycorrhizae are formed with 

 potato by various endophytes some normally present with monocoty- 

 ledonous, some with dicotyledonous plants. The endophytes present 

 in various soils simply grew into the potato roots and gave the stimulus 

 to the production of characteristic tubers. It was the potato plant that 

 determined tuber form, not the fungus. 



The mycorrhizal association, therefore, appears more as a casual 

 thing than as an occult and premeditated action that can be achieved 

 only by special, designated actors. It is true that certain fungi do seem 

 more or less confined to certain mycorrhizal hosts, although specifi- 

 city cannot be said to be absolutely proved ; but a certain amount of 

 specificity could be posited on the grounds of chemical affinities. 

 The emphasis that has been placed on mycorrhizal fungi would seem, 

 therefore, to be somewhat exaggerated because in so many cases 

 the identity of the fungus seems a relatively inconsequential thing. 

 It is nutrient that the higher plant requires and in many cases it seems 

 of little moment whether the particular fungus which supplies the 

 nutrient happens to be a Russula or an Amanita, a Boletus or a Tri- 

 choloma. These are the fungi of the forest floor and naturally have to 

 be the mycorrhizal fungi of the trees that grow there. It would seem 



