Tree Mycorrhiza. 217 



the lines indicated may assist in the ekicidation of the hitherto 

 unsolved question of the true relation that exists between the 

 fungus and the root in the case of ectotropic mycorrhiza. 



Recent literature (1912-1922) points clearly to the fact that 

 from a biochemical and microchemical standpoint investigators 

 differ widely in the interpretation of the results of their work (4). 

 On the one hand it is maintained that the relation between tree 

 and fungus is that of parasitism only on the part of the latter, 

 while on the other hand it is regarded as symbiosis in the broad 

 sense of the term. 



Field studies afford considerable evidence in favour of the 

 view that the relation is something more than that of parasitism 

 and that it is mutual or s>anbiotic. 



Summary. 



[a) The association with a mycorrhizal fungus commences, 

 in the case of birch, while the seedling is very young, almost 

 immediately after germination, and it exhibits no indication of 

 injury, accruing from the fact that the whole of its root system 

 immediately developes mycorrhiza. 



(6) The whole of the water absorbed by such a seedling must 

 pass through the mantle. It contains dissolved colloid sub- 

 stances from the surrounding matrix. Water is readily absorbed 

 and readily yielded by the mantle. 



(r) Roots of woodland trees, oak and beech, for example, 

 creep over the surface of the soil, where there is an abundance 

 of moss, and entering the lower layers of the moss carpet develop 

 mycorrhiza. A chemotoxic action is apparently set up within 

 the decaying moss. 



{d) There are indications that in cases of severe drought 

 when much mycorrhiza has been destroyed, certain trees, 

 notably, birches of all sizes, and hornbeam stools, lose vitality 

 and become specially subject to attacks from microfungi such 

 as Mclanconis stilbostoma (Fr.) Tul. and Pscudovalsa lanciformis 

 (Fr.) Ces. and de Not. (5). 



I am much indebted to Dr Somerville Hastings for the photo- 

 graphs of mycorrhiza in situ and to the Essex Field Club for the 

 loan of two blocks. 



REFERENCES. 



(1) Peklo, J. Epifyticke mykorrhizy. II. Carpinus Betuliis a. Fagus silvatica. 



Rozpravy Ceske Akademie, etc. Thda 11, Rocnik. xix (1910). fislo 35. 



(2) NoACK, F. ijber mykorrhizenbildende Pilze. Bot. Zeit.xLVii, p. 389(1889). 



(3) Peyronel, B. Xouveaux cas de rapports mycorhiziques entre Phanero- 



games et Basidiomycetes. Bull. Soc. JMycol. Fr. xxxvii, p. 143 (1921). 



(4) Ramsbottom, J. Orchid Mycorrhiza. Trans. Brit. Mycol. Soc. viii, p. 28 



(1922). 



(5) Paulson, R. An Enquiry into the causes of the death of Birch Trees in 



Epping Forest and elsewhere. Essex Nat. xi, p. 273 (igoo). 



