Lecture II — 15 — Occurrence of Mycorrhizae 



would be in a much better position to go forward with research if our 

 research were founded on a considerable number of papers like that 

 of Janse's, or even such simple lists as that of Klecka and Vukolov 

 (1935). 



But if we know little of mycorrhizal occurrence, we know even less 

 of root-hair occurrence. Morphologists have never paid much atten- 

 tion to roots except to study the vascular systems of older roots. Roots 

 are in the ground, it takes considerable work to get them out, and the 

 botanist pulls off a twig or a leaf or a flower and goes onward. An 

 herbarium in which a "specimen" always included the root would be a 

 curiosity. A thorough-going study of root structure has yet to be 

 made, especially of the "absorbing" system of smaller rootlets: we 

 still await a Systematic Morphology of Root-endings. 



This statement leads to a consideration of the second reason for 

 studying occurrence of mycorrhizae, namely, their importance. It is 

 obvious that plants take in their nutrient materials through root-hairs 

 or mycorrhizae except for a comparatively small number that are able 

 to live without either. If root-hairs predominate in nature, then 

 physiological research should be directed chiefly to root-hair plants; 

 but if mycorrhizae predominate, then plant physiology should be con- 

 cerned chiefly with mycorrhizae. Botany will some day be forced to 

 a decision in the matter. At present botanists are in a position of 

 ignorance, for they do not know what sort of root endings exist on 

 the majority of plants in their natural haunts. They assume that root- 

 hairs are the usual organs for intake of nutrient materials into plants, 

 but their assumption cannot be substantiated from the records of 

 research. Moreover, there is little prospect that research will be done 

 on such structures, for the ruling motive in botanical science today 

 appears to be a subservience to the authority of tradition. 



The Occurrence of Root-Hairs: — According to Frank 

 ScHWARZ (1883), the first mention of root-hairs is found in Mal- 

 piGHi's Opera Omnia (1681), having observed them in elm, black 

 poplar, and willow and he believed that in their tiny tubes he had be- 

 fore him that in which crude sap ascended and was later led into the 

 vessels. He found them especially in those places where earth was 

 not immediately in contact with roots. When the root hairs then 

 pushed out into neighbouring soil, they grew around individual soil 

 particles and surrounded them, so that they formed a span between 

 the roots and soil particles. A similar clinging of the hairs was de- 

 scribed by Malpighi in the roots of ivy. Almost simultaneously N. 

 Grew (1682), in his "Anatomy of plants", advanced the idea that the 

 spongy ends of roots served admirably for provision with food and 



