S YMBIOSIS. 34 I 



ground, but do not pass beyond the first stages of develop- 

 ment unless in contact with the root of the host by which 

 they are normally sustained. Under these conditions they 

 then form a cone-like enlargement, which unites with the 

 cortex of the host root and penetrates to the stele. From 

 this conical stem arise the aerial shoots. Other parasites 

 form a network or even a complete hollow cylinder outside 

 the wood of the host and under the bark. From this 

 curious body the few flowers break through the bark and 

 appear upon the surface of the root or stem of the host, quite 

 as though they were a part of it (fig. 381). 



