392 RESEARCHES ON FUNGI 



wound-tissue, with which the pseudorhiza heals itself, serves to keep 

 bacteria and other small organisms from making their way into the 

 interhyphal air-spaces and to conserve moisture in dry weather. 



The Mycelium and the Problem of Parasitism. — ^The continuity 

 of a persistent pseudorhiza with the mycelium in the root of a Beech 

 is well shown in Fig. 193 (p. 386) which is reproduced from a sketch 

 made by Miss E. M. Wakefield. The root contained a paper-thin 

 sheet of mycelium between the bark and the wood {n), and a thicker 

 sheet of mycelium in the wood itself (m). With these sheets of 

 mycelium the base of the pseudorhiza was in direct continuity. 

 Moreover, Miss Wakefield found long tubes containing a dense 

 liquid and therefore resembling latex vessels, not only in the 

 pseudorhiza but also in both of the mycelial sheets. These observa- 

 tions, as well as others which there is no need to describe, clearly 

 show that the mycelium of Collybia fusipes inhabits the roots above 

 which the fruit-bodies are found. 



In a few cases I observed that there was a sharp line of demarca- 

 tion between the dead part of a buttress-root upon which the 

 mycelium of Collybia fiisipes was feeding and the living sap-filled 

 part a few inches nearer the tree-trunk. What was observed 

 suggested that the fungus is parasitic on Beeches and Oaks, and 

 that its mycelium is able to kill and destroy progressively even their 

 stoutest roots. On the other hand, it might perhaps be argued that 

 the fungus is nothing more than a saprophyte, and that it destroys 

 roots progressively toward the tree-trunk only after they have died 

 from other causes. To determine mth certainty whether or not 

 Collybia fusipes. in addition to behaving as a saprophyte, may also 

 behave as a parasite would require a detailed investigation such as 

 I have not been able to make. It is possible that, if one inserted 

 small pieces of Beech wood in which the mycelium was growing 

 into a large sound root, the mycelium might grow into the wood 

 of the sound root and kill the root as its hyphae advanced ; and, 

 in a few successive summers, one might observe fruit-bodies coming 

 up above the inoculated root and attached to it by pseudorhizae. 

 If fruit-bodies were thus produced during two or three successive 

 summers, one wovild doubtless find at the end of this time that the 

 root had been killed and its wood destroyed for a distance of several 



