44 MOVEMENTS OF SEEDLINGS. 



vice to them is very doubtful, but with seeds germi- 

 nating on the surface it will slightly aid geotropism 

 in directing the radicles to the ground. We as- 

 certained in one instance that such sensitiveness 

 resided in the tip and caused the adjoining parts 

 to bend from the light. . . .' u 



" We believe that there is no structure in plants 

 more wonderful, as far as its functions are con- 

 cerned, than the tip of the radicle. If the tip be 

 lightly pressed or burned or cut, it transmits an 

 influence to the upper adjoining part, causing it to 

 bend away from the affected side ; and, what is 

 more surprising, the tip can distinguish between a 

 slightly harder and softer object, by which it is 

 simultaneously pressed on opposite sides. If, how- 

 ever, the radicle is pressed by a similar object a 

 little above the tip, the pressed part does not 

 transmit any influence to the more distant parts, 

 but bends abruptly towards the object. If the tip 

 perceives the air to be moister on one side than on 

 the other, it likewise transmits the influence to the 

 upper adjoining part, which bends towards the 

 source of moisture. When the tip is excited by 

 light (though in the case of radicles this was as- 

 certained in only a single instance) the adjoining 



1 pp. 551, 552. 



