﻿MacDougal: The Mycorhizae of Aplectkum 111 



eral arrangement resembles that of the underground stems of Cor- 



allorhiaa. 



The brown hyphae from the mycorhiza of neighboring trees 

 adhere and penetrate the epidermis of the roots in patches in such 

 manner as to make it appear that the Aplectrutn is parasitic upon 

 the trees as suggested by Mr. Gilman. I find, however, that the 

 fungus simply adheres to the roots of both plants and that the 

 Aplectrutn is parasitic upon the tree only in the remote sense that 

 it is a competitor for the organic substances absorbed by the 

 fungal .symbiont from the soil. This last named fungus forms 

 complete coatings on the roots of oaks and maples and penetrates 



Aph 



these are met. 



The variation in the species, which forms the chief interest of 

 this paper, is due to the manner in which the endotropic fungus is 

 transmitted from the parent to young plants through the offshoots- 



The offshoot is usually a cylindrical smooth stem 1-2 cm. in 

 length, consisting of about three internodes. The cortical cells in 

 normal plants are seen to be filled with the hyphal masses in- 

 creasing in number from the apical end of the offshoot toward the 

 younger plant. Since no trichomes are present, the hyphae do 

 not pass outwardly and into the soil. An examination near the 

 base of the offshoot on the lower side reveals a small clump of 

 hairs which are directed downward and toward the roots of the 

 parent plant. The fungus in these roots sends hyphae out into 

 the soil, which, meeting the clump of hairs on the offshoot, pene- 

 trate through them into the cortical tissues, thence penetrating the 

 offshoot lengthwise to the apex, passing into the roots of the young 

 plant directly, since these organs arise from the apex of the off- 

 shoot. By this arrangement the fungus is confined to the absorb- 

 ing organs and does not gain access to the storage tissues of the 

 corm. 



Now, it is to some disturbance in the relations of the fungus 

 in transit through the offshoot that the coralloid formations are 

 due. In such instance the offshoot develops numerous branches 

 consisting of a relatively large number of internodes. The epi- 

 dermis has developed an enormous number of trichomes resem- 



