Mycorrhiza Fungi 



87 



cells other than tliose of the epidermis; there is an extensive intcr- 

 celluhu' de\ elopmcnt between the cortical cells of the roots which is 

 especially characteristic of forest trees. (2) Endotrophic mycorrhiza, 

 in which the hyphae of the fungus penetrate to the inner parts of 



Fic. 41. Ectotropliic mycorrhiza growing in flask culture (from Melin). 



the roots, into definite root layers, and into the cells, and have little 

 connection with the mycelium in the soil. This is true of plants 

 belonging to the Orchidaceae, Ericaceae, and Eparidaceae, and 

 is now known also for many other plants. Root hairs are frequently 

 absent in ectotrophic mycorrhiza and are replaced by hyphae of 

 fungi. 



Melin described three types of mycorrhiza formations on pine 

 trees: (1) Forked mycorrhiza, best developed in the presence of an 

 abundant layer of raw humus; it is golden-brown to black in color. 

 (2) Tuber mycorrhiza, which is pale at first and later becomes gray 

 to brownish gray. (3) Simple mycorrhiza, or the unbranched form 

 characteristically found on the pine; this may be a young stage of 



