SAPROPHYTISM AND SYMBIOSIS 337 



evidence of the parasitism of some fungus on the tree. 

 Several species of fleshy fungi are, in this way, parasitic 

 or partly parasitic. In ectotrophic infection the hyphae 

 penetrate through the epidermis and then grow and branch 

 underneath it, some of the branches growing between the 

 individual epidermal cells by dissolving the middle lamella 

 with enzymes which they secrete. In this manner there 

 is formed a pseudo-tissue, closely analogous to a lichen, 

 which replaces the true epidermis. The fungus doubtless 

 derives some nourishment from the dissolved (digested) 



Fig. 245.— Tangential section of root of the red maple {Acer rubrum), 

 showing endotrophic micorhiza in the cells. (After W. B. McDougall.) 



substance of the middle lamella, as well as from nutrient 

 substances that diffuse out from adjacent cells; but there 

 is no evidence that the tree is in any way benefited by the 

 presence of the fungus. 



In some cases the development of the mycorrhiza- 

 mantle inhibits the growth of the root, and stimulates a 

 profuse branching, which is repeated as the branches are 

 infected. This gives rise to a malformation known as 

 ''coral root," which is so well developed in one herbaceous 

 species as to give the plant its scientific as well as its 

 common name — Corallorhiza, or coral-root. 



In endotrophic mycorrhizas the hyphae penetrate 

 through the cell-walls into the cell-cavities, and in such 



