1 9 6 



BOTANY OF THE LIVING PLANT 



Sarcodes) (Fig. 148). In the last-named, which is a complete sapro- 

 phyte native of the Western States of America, the root-cap is shed 

 off in layers, which are held in the fungal weft. This closely invests 

 the superficial cells of the root, forcing them apart ; but still they 

 appear healthy and active. The fungal filaments do not as a rule 

 penetrate the cells themselves, so that the investment is external. 

 It is, however, so complete when fully developed that the surface of 

 the root has no direct contact with the soil, and takes its supplies 

 through the medium of the fungus. The hyphae at the outer surface 

 grow out into absorptive filaments that take the place of the root-hairs. 



FIG. 148. 



Part of the superficial tissue of a root of Sarcodes, covered by a dense felt of 

 fungal hyphae (h), in which the dark lines (r, o) are the layers of the root-cap 

 The fouterrnost layer of cells of the cortex (c) is covered by a pihferous layer (e), 

 bufthe root-hairs are replaced by conical cells between which the fungal hyphae 

 have forced their way. (After Oliver.) 



The native Monotropa hypopitys, which grows in woods of Fir and 

 Beech, is also a complete saprophyte. Its only visible means of 

 nutrition is from the decaying vegetable matter in which it lives, 

 through the intermediary of the symbiotic fungus. This is found 

 closely investing the surface of its roots, and occasionally penetrating 



the cells. 



In estimating the relations of the two parties to ectotrophic myco- 

 rhiza in green plants, one essential fact is that it is not a necessary 

 condition of the life of the tree, nor does the fungal investment neces- 

 sarily cover the whole root-system. Experimental cultures have 

 given contradictory results as to the benefit derived by the higher 

 Plant. But certain general considerations seem clear. On the 



