Lecture II — 23 — Occurrence of Mycorrhizae 



Hyphae have also been observed in antheridia and in canal cells of 

 the archegonium but never in the egg-cell. 



The work on Psilotiini has presumably been done on P. trique- 

 trum from which we may turn to the other genus of the family, 

 Tmesipteris, a genus of Australian herbs. In the first of several papers 

 on mycorrhizae, Dangeard (1891) described endotrophic mycorrhizae 

 from five species of Tmesipteris, telling of the fungi and their appear- 

 ance in the root ; and it would seem that he may have been dealing with 

 both parasitic and mycorrhizal fungi. But he describes and figures 

 Hartig net, hyphal coils, and notes disappearance of starch from the 

 infected region. It is curious that the useful term, "mycorrhizome", 

 should have been invented for the service of these plants so little 

 known to the general botanical public; yet Dangeard said that as 

 roots are wanting in these plants, they may be said to possess mycor- 

 rhizomes. So came into being a designation for all endophytic creep- 

 ing stems, especially amongst ferns and orchids. 



The gametophyte of Tmesipteris, like that of Psilotum, contains 

 an endophyte ; for Lawson (1917) in a paper complementary to that 

 of Darnell-Smith described the infection in T. tannensis. Structu- 

 rally the prothallium of Tmesipteris does not resemble that of Ly co- 

 podium but it does that of Psilotuin. 



Gymnospermous Mycorrhizae : — In all classes of Gymncsperms 

 there are found mycorrhizal fungi occurring as endophytes. Among 

 all the branches of the plant kingdom, none has attracted more re- 

 search than that of the conifers ; and especially have the pines been 

 investigated. As early as 1865 Nicolai had unwittingly described the 

 mycorrhizal character of pine rootlets although it was not until 1873 

 that Reinke remarked the similarity of the cortical "thickenings" of 

 the pine rootlets to those of the liverworts known to be due to fungi. 

 Several reasons may be adduced for predilection for pine mycorrhizal 

 research : first, modern mycorrhizal research began with the pines ; 

 second, the pines are easily studied ; third, they are of great economic 

 importance. About one-fifth of all mycorrhizal research in the last 

 decade has been done with Gymnosperms, and of these principally 

 pine, spruce and fir. 



Mycorrhizae of Gycads: — Tubercles of the Cycads appear to 

 harbour both fungi and bacteria and are modified rootlets. For them 

 the name of "consortium" has been proposed, a name first suggested 

 by Grisebach according to Reinke (1871) who quaintly observed 

 that the term is "sehr zutreffend". Life, who made an extended study 

 of these "consortia", declared that "In reference to the symbiotic rela- 



