328 Life and Immortality. 



from the tip, we should, however, remember that it is the tip 

 that is sensitive to the contact of hard objects, causing the 

 radicle to bend away from them, thus directing it along cer- 

 tain lines in the soil where the least opposition interposes. It is 

 again the tip that is alone sensitive, at least in some instances, 

 to moisture, causing the radicle to bend towards its source. 

 These last two kinds of sensitiveness conquer for a time the 

 sensitiveness to geotropism, which, however, ultimately pre- 

 vails. But the three kinds most often come into antagonism, 

 first one prevailing, and then the other. It would, therefore, 

 be an advantage, perhaps a necessity, for the interweighing 

 and reconciling of these different kinds of sensitiveness, 

 that they should all be localized in the same group of cells 

 which have to transmit the command to the adjoining parts 

 of the radicle, necessitating it to bend to or from the source of 

 the irritation. 



Though generally believed by authors that the modifica- 

 tion of the upper or lower surfaces of a radicle, whereby 

 curvature is induced in the proper direction, is the direct 

 result of gravitation, yet there can be no question from all 

 that has been said that it is the tip alone that is acted on 

 and that transmits some influence to the adjoining parts, 

 causing them to curve in a downward manner. Gravity, it 

 would seem, does not act in a more direct way on a radicle 

 than it does on any lowly-organized animal, which moves 

 away when it feels some weight or pressure. 



When we consider what we have written, it is impossible 

 not to be impressed with the resemblance between the move- 

 ments of plants and many of the actions performed by the 

 lower animals. With plants an astonishingly small stimulus 

 suffices. One plant may be highly sensitive to the slightest 

 continued pressure, while a closely-allied form just as highly 

 sensitive to a slight momentary touch. The habit of moving 

 at certain periods is inherited both by plants and animals ; 

 and other points of similitude have been specified. But 

 the most striking resemblance is the localization of their 



