MacDougal: Svmiuosis akd Saprophytism 



515 



proper. • The two types of roots show a remarkable resemblance 

 in stelar alterations to those of the two types in Wulhchlacgdm 

 aphylla as described by Johow (7, p. 427), though not so distinctly 

 separated by external characters. 



The older roots often assume a dark -brown color over certain 

 regions 6-10 cm. in length, due to the presence of an ectotropic 

 fungus, which forms a permanent myceliuui in three or four of the 

 outer layers of the cortex (see page 523). The hyphae are heavy 

 walled and septate. The inner branches form large vesicles which 

 occupy the greater part of the cells of the medio-cortex. The outer 

 branches of the mycelium pass through the short root-hairs ' 

 the soil. The region inhabited by the fungus gives rise to a few 

 rootlets which assume the form of lozenge shaped branches with 

 a len<^th not greater than 3 cm. These branches arise endogcn- 



mto 



ously, are brownish to within a few millimeters of the tips and are 

 furnished with a well developed root cap. The mycorhizal fun- 

 gus advances toward the tips as in the branches of the Coral- 

 lorhha, and the entire structure shows an arrangement generally 

 similar to the coralloid branches of that plant. 



In the half dozen perfect specimens in the hands of the writer 

 the branches arise only from regions inhabited by the fungus and 

 it is conjectured that the presence of this organism may act as a 

 stimulant in setting up such action. The fungus is found in por- 



\ 



Fig. I. Mycorhizal portions of roots of Cephalanthera. 



tions of the root-system 50 to 60 cm. below the surface of the 

 soil, and as these organs are very brittle, especially the mycorhizal 

 portions they are generally broken off in collection. The absence 

 of chlorophyll and mycorhizas from numerous specimens sent in 

 by the most careful collectors led the writer to announce that the 



