422 RESEARCHES ON FUNGI 



its upper side than on its lower. The opposite geotropic reactions 

 of the subterminal and terminal parts of the pedicel produce two 

 opposite curvatures which together give to the last 0-2 mm. of the 

 pedicel its characteristic sigmoid form. The sigmoid curvature, 

 since it is due to the positive and negative geotropic stimuli, is 

 necessarily always in a vertical plane (Figs. 205, C, p. 408, and 

 212, E, F). 



That the stimulus of gravity is the true cause of the sigmoid 

 curvature of the end of the pedicel and of the asymmetrical growth 

 of the apophysis of the gemma is strongly supported by an experi- 

 ment made with the help of a Pfeffer klinostat. A malt-agar plate 

 upon which the rudiments of gemmifers of Omphaliaflavida were just 

 beginning to appear was rotated on the klinostat in a vertical plane, 

 and the rotation was continued for several days until the gemmifers 

 were full-grown. As a control, another malt-agar plate, prepared in 

 the same way as the first, was kept in a fixed position (upside down 

 on a table). In the control, when the experiment came to an end, 

 all the gemmae were turned slightly downwards on the ends of the 

 pedicels and, when the gemmae were pulled off their pedicels, the 

 ends of the pedicels were found to have the characteristic sigmoid 

 curvature. Moreover, the gemmae had become asymmetrical in 

 form, the upper side of the apophysis, as usual, having become longer 

 than the lower. On the other hand, in the culture rotated on the 

 klinostat, the ends of the pedicels were quite straight and none of them 

 had developed even a trace of a sigmoid curvature, so that each 

 gemma occupied a symmetrical position on the end of its pedicel. 

 Furthermore, each of the gemmae which had been rotated on the 

 klinostat, instead of displaying the usual asymmetry, was sym- 

 metrical in form, like a door-knob, the apophysis not having 

 elongated more on one side of the gemma than on the other. 



From the above observations and experiments we may conclude 

 that the abscission of a gemma from its pedicel is effected by the 

 end of the pedicel, toward the close of its development, taking on 

 a sigmoid form, and that the sigmoidal curvature is due to the end 

 of the pedicel giving a double response to the stimulus of gravity. 

 It is evident that a gemmifer is beautifully organised as an organ 

 for the production and liberation of its gemma. 



