OMPHALIA FLAVIDA 421 



the pedicel is becoming sigmoid that the top of the pedicel is torn 

 away from the gemma, thus bringing about the abscission of the 

 latter. After abscission of the gemma has been effected, the 

 attachment of the gemma to the pedicel is maintained merely by 

 the clasping apophysis (c/. Fig. 212, E). 



Until the abscission of the gemma has taken place, the apophysis 

 firmly clasps the pedicel, and it is this firm attachment which makes 

 abscission of the gemma from the top of the pedicel mechanically 

 possible. After abscission has taken place, the attachment of the 

 apophysis to the pedicel weakens, and then the gemma can readily 

 be blown off the pedicel by the wind (Fig. 212, F). Thus the apophy- 

 sis functions in two ways : ( 1 ) it grasps the pedicel subterminally 

 and thus permits of the abscission of the gemma from the top of the 

 pedicel, and (2), after abscission, it holds the gemma on to the top 

 of the pedicel until a blast of wind carries the gemma away and thus 

 brings about its dispersion. 



We have just seen that the sigmoidal growth-curvature of the 

 end of the pedicel results in the abscission of the gemma from the 

 top of the pedicel. We may now ask : what causes the end of 

 the pedicel to assume its sigmoid form ? The answer to this 

 question is to be found in the response of the pedicel to geotropic 

 stimuli. 



By observing gemmifers growing on malt-agar plates from 

 surfaces looking upwards, downwards, and sideways, it was found : 

 (1) that the part of the pedicel in the region of the collar of the 

 apophysis always bends downwards through an angle, often of 45°, 

 during the last stages of the development of the gemmifer ; (2) that, 

 at the same time, the very top of the pedicel, hidden within the 

 apophysis, always bends upwards (Fig. 212, E) ; and (3) that, whilst 

 the pedicel is bending sigmoidally, the upper side of the apophysis 

 elongates slightly more than the lower (Figs. 205, C, p. 408, and 

 212, E). The simplest explanation of all these growth phenomena 

 is that they are due to geotropic stimuli : gravity stimulates the 

 pedicel in the region of the collar of the apophysis to elongate more 

 on its upper side than on its lower ; gravity stimulates the pedicel 

 at its very top to elongate more on its lower side than on its upper ; 

 and, finally, gravity stimulates the apophysis to elongate more on 



