Lecture I — 11 — Rise of Mycotrophy 



pounds ordinarily taken in by root-hairs, and growth promoting sub- 

 stances, thiamin, nicotinic acid . . ." 



Phagocytosis : — Whatever may be finally decided as to the nature 

 of the mycorrhizal symbiosis, it is observed that something is released 

 in the tissues of the higher symbiont by the fungus. It is becoming 

 increasingly evident that in what are termed "digestion cells" of the 

 host the hyphae break down and disgorge their contents, the matter 

 being digested and assimilated by the host. Since it is a cellular diges- 

 tion, Bernard called it a phagocytosis; but the whole process had 

 been pictured and to some extent described long before Bernard. 

 In 1943 it was suggested by Kelley that the whole mycotrophic rela- 

 tion depends on a balancing of ionic concentrations between fungus 

 and higher plant. 



Phycomycete Mycorrhizae: — While the majority of mycor- 

 rhizal fungi are basidiomycetes, it is now recognized that in many 

 mycotrophic symbioses the fungus is a phycomycete. Such symbioses 

 were studied in earlier years especially by Peyronel. Rayner, in 



1935, commented on the "remarkably wide geographical distribution 

 of this 'Phycomycete type' of mycorrhizal association, its prevalence 

 in plant species of the most diverse affinities, together with its re- 

 corded appearance in certain crop plants. . ." Other more recent 

 studies of the phycomycete mycorrhizae include those of Biraghi in 



1936, on cereal grains. Bain in 1937 on cranberry, Sabet in 1939 on 

 cotton, and Ruggieri in 1937 on Amygdahts. Butler in 1939 pre- 

 sented a paper summarizing what was then known of this sort of 

 mycorrhiza, terming it the vesicular-arbuscular mycorrhiza and 

 grouping the endophytes under the generic name of Rhizophagus. 



Forest Tree Mycorrhizae: — Although so much work has been 

 done on forest tree mycorrhizae, knowledge concerning them is still 

 defective. Considerable is known of those that occur on pine, spruce, 

 larch, beech and some others, but researches upon them have been 

 done by a few individuals working with limited material. The 

 extent of mycorrhizal occurrence, both taxonomic and geographical, 

 is still a matter of conjecture and, as most of mycorrhizal research 

 has been done in Europe, the forests of the other continents are for 

 the most part still uninvestigated by students of this science. Moreover, 

 the natural difficulties in the way of isolating the mycorrhizal fungi 

 make for ignorance of the symbiosis, for the syntheses of seedlings 

 and fungi in pure cultures show merely what man can achieve and 

 not what occurs naturally in the forest. Then, too, the nutrition of 



