420 RESEARCHES ON FUNGI 



mycelium. There can be no doubt, therefore, that the basal 

 curvature of the pedicel is not due to a geotropic stimulus. 



What, then, does cause the basal curvature of the pedicel ? A 

 study of the disposition of gemmifers in a single group growing on 

 agar in upright, inverted, or vertical fixed Petri dishes or in Petri 

 dishes rotated in a vertical plane on a klinostat, or on a leaf-spot 

 (Fig. 213), reveals the fact that the gemmifers diverge from one 

 another. One cause of the general curvature of the stipe, therefore, 

 is the mutual repulsion of the gemmifers. Where a gemmifer is 

 growing alone and its pedicel is curved, it may be that the 

 curvature is due to the mycelium in the substratum which in some 

 way repels the gemmifer more on one side than on the other. 



The bending of the stipe of a sporophore and the basal bending 

 of the pedicel of a gemmifer are due to different causes and have 

 different biological advantages. A stipe is negatively geotropic : 

 as it grows in length, its upper end becomes more and more vertical, 

 with the result that the median axis of the pileus becomes vertical 

 and the pileus is given the most favourable orientation for the 

 successful discharge of the spores (Fig. 213, p. 424). On the other 

 hand, a pedicel (except at its apex, as we shall see in the next Section) 

 is ageotropic and the different pedicels in a group of gemmifers bend 

 away from one another owing to mutual repulsion, with the result 

 that the gemmae, which are adhesive, avoid coming in contact with 

 one another during their development and, when the time arrives 

 for their dispersion, have a better chance of being carried off freely 

 by the wind (Fig. 213). 



The Sigmoid Curvature of the Pedicel and the Abscission of the 

 Gemma. — A gemma, before being dispersed by the wind, undergoes 

 abscission from the end of the pedicel whilst still attached to the 

 pedicel subterminally by means of the clasping collar-like apophysis 

 (c/. Fig. 212, D and E). The abscission process, which is effected 

 in a unique manner, has been investigated in detail, and an account 

 of it will now be given. 



The extreme end of a pedicel (the last 0-2 mm.), i.e. the part 

 within and just below the clasping apophysis, is at first quite 

 straight (Fig. 212, D) ; but, finally, as shown in Figs. 205, C (p. 408) 

 and 212, E, it becomes curved sigmoidally. It is whilst the end of 



