Kelley 



— 124 — 



Mycotrophy 



hairs ; they elongate in an obHque direction at an angle of 45° with 

 the axis of the root and their length attains the double or the triple 

 of their diameter. He notes that, whereas in cupulifers only the 

 epidermis is involved, in beech, etc., two layers of cells are hyper- 

 trophied ; while in pine, fir, larch, a great number of layers are affected. 

 In any case, hyphae intrude between walls of the cells, — dissolving 

 out the cementing pectate and forming "palmettes" which may cover 



Fig. 9. — Cross-section of an ectotrophic mycorrhiza of Quercus 

 montana, indicating mantle or mycoclena and cortical cells filled 

 with endophyte. {Original draiving from a slide prepared by Dr. 

 K. D. Doak). 



the radial face of the cell. MacDougal & Dufrenoy (1944) state 

 that in pine the middle lamella of the outer cortex is traversed. Seen 

 in section the intruded hyphae between the cortical cells appear as a 

 netted structure which has been called the "Hartig net" after Th. 

 Hartig who early observed it, although he supposed the structure 

 was composed of anastamosing canals. 



Besides in cupulifers, ectotrophic mycorrhizae occur in ericads 

 and some other plants. Hesselman described such structures from 

 the arctic Salix herbacea and in the herbaceous Dryas octopetala and 



