THE PERENNIAL PSEUDORHIZA 393 



feet. The rate of progress of the mycelium along the root per 

 annum might then be calculated. If such a series of positive 

 observations should one day be made, there would be no alternative 

 but to regard Collybia fusipes as a destructive root-parasite. On 

 the other hand, if inoculation experiments were to yield only negative 

 results, we might be obliged to consider the fungus merely as an 

 innocent saprophytic scavenger, which rots Beech roots and Oak 

 roots only after these have been killed by some other agency. 

 Here, then, is an attractive problem for the phytopathologist. 



The Functions of the Pseudorhiza and the Significance of its 

 Persistency. — The pseudorhiza of Collybia fusipes has the same 

 chief function as the pseudorhiza of Collybia radicata, Coprinus 

 macrorhizus, etc., i.e. it serves as an organ for pushing upwards 

 from the surface of the buried nutrient substratum (here a tree- 

 root) through a non-nutrient medium (here soil and leaf-mould) to 

 the surface of the ground the rudimentary stipe-shaft and pileus, 

 thus enabling these parts of the fruit-body to expand subaerially. 

 The pseudorhiza also (1) conducts food materials from the mycelium 

 in the buried root to the stipe-shaft and pileus whilst these are 

 developing subaerially, and (2) gives a certain amount of mechanical 

 support to the aerial stipe-shaft and pileus, thus assisting these 

 organs in taking up and maintaining their proper positions in space. 



Just as in Collybia radicata and Coprinus macrorhizus, the 

 pseudorhiza of Collybia fusipes increases in length bj^ intercalary 

 growth in a subterminal axial region which lies just below the 

 rudimentary pileus and stipe-shaft. The upward direction of 

 growth of the pseudorhiza is doubtless due to negative geotropism ; 

 and probably the pseudorhiza, while able to grow in length freely 

 in the dark soil, has its growth in length inhibited by light, so that 

 the action of light regulates the length of the pseudorhiza and 

 prevents this organ from emerging above the surface of the ground. 



In Collybia radicata and C. longipes the pseudorhiza is strictly 

 annual and dies shortly after the fruit-body of which it forms a 

 part has shed its spores, but in Collybia fusipes it is perennial. In 

 having a perennial pseudorhiza Collybia fusipes, so far as is at 

 present known, is not only unique in the genus Collybia but also 

 unique among the Agaricaceae in general. 



