LECTURE XI 



THEORIES OF MYCOTROPHY 



Contrasted Concepts: — There are two contrasted concepts of 

 the endophytic relation, first, that the fungus is a parasite on its host, 

 and second, that the two symbionts live in some sort of a mutualism. 

 Of 118 papers in which the writers expressed a definite opinion about 

 the endophytic relationship, fourteen voted for parasitism. To some 

 extent these opinions were based on personal bias rather than on ex- 

 periment, and it remains evident that most investigators who have 

 worked experimentally with endophytic structures conclude that the 

 relationship of fungus to host is beneficial to at least the higher plant. 

 But the views of the others deserve consideration, especially since in 

 a number of cases the divergence in opinion is after all a divergence 

 in viewpoint, and in the last analysis both sides are found in essential 

 agreement. 



Parasitism: — Those who concluded from a morphological study 

 that the relationship is a parasitism include : Cavara ( 1893) , Chodat 

 & Lendner (1896), GiBELLi (1883), Goebel (1888), McDougall 

 (1914 et seq.), Masui (1926), Prat (1934), and Robert Hartig 

 (1888), who was decidedly opposed tO' Frank's ideas of mycotro- 

 phism. He based his opinion chiefly on the alleged observation that 

 trees in nature have young roots that are entirely immune to the 

 fungus, and that mycorrhizae are more or less exceptional. "I have 

 shown above", said Hartig (p. 118) "That mycorrhizae are not 

 always present, that not a trace of a mycorrhiza was to be found on 10- 

 year old oak, beech, hornbeam, hazel, in the experimental garden of 

 the Forest Institute, which were carefully excavated, that a relatively 

 large number of roots of native trees which were carefully studied 

 were found to be fungus free, and that there is not a single fact 

 which would lead to the belief that cupulifers, conifers, ericads, etc., 

 have so remarkably different a mode of nutrition from that of other 

 trees. I see in mycorrhizal fungi nothing more than parasites which 

 live on the tree but do not kill it, just as there are countless parasites 

 which live on the leaves without injuring them." Much of the preju- 

 dice against mycotrophy which has existed to this day comes from 

 this positive statement of Hartig. Such is the power of dogmatism. 



