LECTURE X 

 OBLIGATE SYMBIOSIS 



Fungi and Trees: — That fungi are confined in their symbiosis 

 to one species of plant was stated as early as 1841 by Tulasne, who 

 said that Elaphomyces granulatus was confined to one species of tree ; 

 and GiBELLi in 1883 suggested that the mycorrhizal condition is a 

 necessary one in the cupuliferae. In more recent years the confine- 

 ment of certain fungi to the neighbovirhood of certain trees has been 

 remarked. Thus, Barsali (1922) found that in forests about Pisa 

 there were always the following fungi associated with the trees named : 

 Lactarius delicosus under Pinns Pinea on sandy soils (but Romell, 

 1939, said that this fungus is rarely found with pine) ; L. volemus and 

 L. oedomatopus under P. pinaster; Boletus boviiius under P. pinaster 

 and Jiiniperus macrocarpa; B. granulatus under P. pinaster; B. 

 edidis under Quercus and Castanea; B. corsicianus under Q. ilex 

 (where this species grows with Q. Suher) ; Rnssida grisea and R. 

 emetica together with Lactarius under P. pinaster. Lange (1923) 

 gives a comparable list for Denmark, and Lidl (1939) for Germany. 

 Palm (1930) had noted a Boletus growing in association with P. 

 Merkusii in forests of Sumatra and another bolete under P. cubensis 

 in the Guatemalean highlands. Young (1937) found both Rhiao- 

 pogon luteolus and Boletus granulatus under the same pine tree in 

 Queensland, and thought it possible that both are symbionts of the 

 same tree at the same time. Reess (1885) had concluded that Elapho- 

 myces is dependent for its occurrence on presence of pine. Again, 

 Hammarlund (1923) noted association of Boletus with Larix in 

 Sweden, and proved by synthesis that the fungus is mycorrhizal. 



Ecological Influences: — An interesting ecological study of such 

 occurrences was made by Peyronel (1917) : (i) in Larix decidua 

 woods, boleti predominate; (2) in cupuliferous woods agarics pre- 

 dominate, especially polypores ; (J) with Salicaceae, Populus treniula 

 has a rich fungal coterie while Salix alba has none; (4) Betida alba 

 is accompanied by a discrete number of humus fungi, while Alnus 

 glutinosa is found with Lactarius; but A. viridis lacks characteristic 

 humus fungi ; (5) most other ligneous species are never accompanied 

 by humus-dwelling hymenomycetes ; (6) meadows are characterized 



