iv Movement and Nervous Action in Plants 69 



equal growth explain some of the facts, it seems to others 

 more convenient to take refuge in the hypothesis that there 

 are in longitudinal rows along the moving shoot certain 

 cells which retain the power of contracting and expanding 

 of passing rapidly from one state of water-tension to 

 another and that these determine the movement of the 

 whole shoot. 



For our present purpose what is especially important is 

 that we appreciate the plant world as living ; instead, there- 

 fore, of here prolonging our discussion of the theories held 

 in regard to the movements of climbers, let us return to the 

 general standpoint of Darwin's volume, of which the last 

 paragraph may be quoted : 



" It has often been vaguely asserted that plants are dis- 

 tinguished from animals by not having the power of move- 

 ment. It should rather be said that plants acquire and dis- 

 play this power only when it is of some advantage to them ; 

 this being of comparatively rare occurrence, as they are 

 affixed to the ground, and food is brought to them by the 

 air and rain. We see how high in the scale of organisation 

 a plant may rise when we look at one of the more perfect 

 tendril-bearers. It first places the tendrils ready for action, 

 as a polypus places its tentacula. If the tendril be dis- 

 placed, it is acted on by the force of gravity and rights itself. 

 It is acted on by the light, and bends towards or from it, 

 or disregards it, whichever may be most advantageous. 

 During several days the tendrils or internodes, or both, 

 spontaneously revolve with a steady motion. The tendril 

 strikes some object,' and quickly curls round and firmly 

 grasps it. In the course of some hours it contracts into a 

 spire, dragging up the stem, and forming an excellent 

 spring. All movements now cease. By growth the tissues 

 soon become wonderfully strong and durable. The tendril 

 has done its work, and has done it in an admirable manner." 



