Lecture I — 5 — Rise of Mycotrophy 



roots are formed in humus; Tulasne in 1841, that tree roots were 

 found frequently surrounded by mycelium of the truffles fungus; 

 while Gasparini in 1856 stated that a fungal mantle was found about 

 roots of chestnut, hazel and pine. Hairs were considered so inevitably 

 present on roots that it was heresy to speak of anything else, hence 

 ScHACHT in 1860 cautiously stated that, while root-hairs are present 

 on such trees as oak and beech, they were less abundant on pine and 

 fir. ScHWARZ, from whom we have already quoted, presented a 

 list of conifers from which they were lacking. 



Discovery of the Hartig Net: — When coniferous rootlets 

 were examined in section it was seen that the wall possessed what 

 was termed a peculiar cell-wall thickening; and it is an odd fact 

 that morphologists beheld fungal mycelium in such rootlets for a 

 long time without being aware of its nature. Thus, Nicolai in 1865 

 gave a tolerable description of what is now known as Hartig net 

 without realizing that he was describing a foreign organism in the 

 conifer. Van Tieghem in 1871 also described these "thickening 

 bands" ; and he noticed furthermore that the penultimate layer of 

 root cortical cells was filled with a solid deposit, a fact of significance 

 in mycotrophic nutrition of these conifers. It remained for Reinke 

 in 1873 to call attention to the similarity of these supposed thickenings 

 to mycelial strands which Gottsche had found in the liverwort, 

 PelUa. With realization that tree rootlets were characteristically 

 invaded by hyphae, specific infections were described. Thus, Boudier 

 in 1876, described Elaphomyces on birch, oak and chestnut roots; and 

 he noticed furthermore that such roots were found in acid but not 

 in alkaline soils. 



Nature of Mycotrophism : — The nature of the fungus-host 

 relation was next considered. That the fungus in the root was a 

 harmless parasite was the opinion of Resa, expressed in 1878; and 

 GiBELLi in 1873 had the same opinion. But Reess, publishing in 

 1880, questioned whether the fungus was a parasite on the tree-root 

 or a saprophyte on soil humus. The supposed parasitism of some 

 plants which live in rich humus, such as the Burmannias, had been 

 questioned by Cruger in 1848; and clear recognition of saprophytes 

 as distinct from parasites had been made by Solms-Laubach in 

 1868. By a shrewd guess, Pfeffer in 1877 came to the conclusion 

 that saprophytes actually make use of the materials of humus. With- 

 out experimental evidence, he inferred that mycorrhizal fungi ob- 

 tained nutrient material from the humus and transferred it to the host 

 plant which, of itself, was incapable of utilizing the otherwise un- 



