THE PSEUDORHIZA OF COLLYBIA RADICATA 351 



and also the root of a Horse Chestnut to which they were attached 

 without breaking the connexions (Fig. 175, A). In Queen's Cottage 

 Grounds, Kew Gardens, I found a fruit-body attached to the top 

 of a Beech stump (Fig. 175, C). 



The length of a pseudorhiza varies with the depth of the soil 

 overlying the infected root, through which the rudiments of the 

 pileus and aerial part of the stipe must be pushed up. The deeper 

 the overlying soil, the longer is the pseudorhiza, and vice versa. 

 If a fruit-body begins to develop 16 cm. below the surface of the 

 soil, the pseudorhiza becomes 16 cm. long (Fig. 175, A) ; if a fruit- 

 body begins to develop 7*5 cm. below the surface of the soil, the 

 pseudorhiza becomes 7-5 cm. long (B) ; while, if a fruit-body 

 develops on the top of a stump where the soil is very thin, the 

 pseudorhiza scarcely comes into existence at all (C). It is probable 

 that here, just as in Coprinus sterquilinus} light regulates the length 

 of the pseudorhiza by inhibiting the growth in length of the pseudo- 

 rhiza as soon as this organ has pushed up the rudimentary pileus 

 and aerial part of the stipe to the surface of the ground and has 

 thus come into a position to receive a light stimulus. 



The pseudorhiza thickens and becomes fusoid just beneath 

 the surface of the ground. It is this fusoid portion only which 

 functions mechanically in supporting the weight of the whole of the 

 subaerial part of the fruit-body. The long tapering extremity of 

 the pseudorhiza, which is very thin and weak, merely serves for 

 the conduction of food materials. The principle of economy in 

 structure is here illustrated once more, for the thickening and 

 mechanical strengthening of the pseudorhiza is limited to that 

 part alone which has a mechanical function to perform. 



The pseudorhiza and the aerial stipe-shaft are both solid, their 

 central parts being filled with white fibrils ; and both of these 

 organs are smooth on the exterior (Fig. 175, B). The pileus has 

 a somewhat slimy pellicle ; but, as experiment showed, drops of 

 rain-water are not absorbed through it. The fruit-bodies persist 

 for some time after their expansion, and the spore-discharge period 

 probably lasts for a week or ten days. The discharge of the spores 

 from beneath the pilei is represented in Fig. 175. 



1 These Researches, Vol. IV, 1931, pp. 112-117. 



