Lecture 11 — 17 — Occurrence of Mycorrhizae 



mata or mycorrhizae, but in all cases the relationship appears essen- 

 tially the same. 



Symbiosis among Algae: — Mutualistic symbiosis of fungi with 

 algae, so far as known, is confined to lichens. While it is still main- 

 tained by some people that the lichen symbiosis is a parasitism of the 

 fungus upon the alga, the balance of favour is with the Schwenden- 

 erian theory of mutualism. The algae, principally Cyanophytes and 

 protococcid Chlorophytes, supply organic material, presumably sugary 

 carbohydrates, to the fungi which take in water and dissolved salts 

 from the exterior into the lichen body and thus to the enmeshed algae. 



The lichen body is a thallus but it differs radically from the myco- 

 thallus of the liverwort, which is a tissue containing hyphal strands. 

 In the lichen thallus the chlorophyll-bearing thalloid cells (algae) are 

 discrete or loosely massed together (gonidia), not forming a tissue as 

 in the liverwort ; and the lichen thallus is for the most part a specially 

 and characteristically formed mycelium. Then, too, the fungal sym- 

 biont of the lichen thallus produces reproductive structures (spores 

 and soredia) while in a true mycothallus the fungus does not produce 

 reproductive bodies. 



Mycothalli among Liverworts: — Widespread occurrence of 

 fungal symbiosis amongst liverworts has been demonstrated by the 

 twenty-six investigators who, in the course of history, have studied 

 mycothalli. It is to be assumed that anything so lacking in obvious 

 utilitarian interest as a liverwort should attract but little general regard. 

 It was apparently Schleiden who in 1839 first described what we 

 know as fungal infection of a liverwort (Pellia), — not Leitgeb (1879) 

 as has been erroneously stated ; but as Schleiden did not realize what 

 he had seen, Gottsche (1858) may be termed the real discoverer of 

 mycothallism. In old thalli of Pellia epiphylla and of Preissia com- 

 mufafa he found a branched system of threads going from cell to cell 

 which he at first considered as an individual vascular system but later 

 recognized as fungal. Earlier in the history of mycorrhizal study it 

 was supposed that fungi are commonly associated with the Junger- 

 manniaceae (Leafy liverworts) but absent from the Marchantiaceae 

 (Thalloid liverworts). Such at least was the opinion of Ncmec 

 (1899), who supposed that the Marchantiaceae, being starch pro- 

 ducers, could not have endophytes ; and Stahl (1900) seized upon 

 this erroneous suggestion and wove it into his ingenious hypothesis 

 of mycotrophism. But it was soon made clear that symbiotic fungi are 

 constantly found in many of the Thalloid liverworts. 



