204. CONCLUDING REMARKS. Chap. V. 



in travelling to or from the light. On the other 

 hand, in a few instances tendrils bend towards the 

 dark. 



Fourthly, we have the spontaneous revolving move- 

 ment which is independent of any outward stimulus, 

 but is contingent on the youth of the part, and on 

 vigorous health ; and this again of course depends on 

 a proper temperature and other favourable conditions 

 of life. 



Fifthly, tendrils, whatever their homological nature 

 may be, and the petioles or tips of the leaves of leaf- 

 climbers, and apparently certain roots, all have the 

 power of movement when touched, and bend quickly 

 towards the touched side. Extremely slight pressure 

 often suffices. If the pressure be not permanent, the 

 part in question straightens itself and is again ready 

 to bend on being touched. 



Sixthly, and lastly, tendrils, soon after clasping a 

 support, but not after a mere temporary curvature, 

 contract spirally. If they have not come into contact 

 with any object, they ultimately contract spirally, after 

 ceasing to revolve ; but in this case the movement is 

 useless, and occurs only after a considerable lapse of 

 time. 



With respect to the means by which these various 

 movements are effected, there can be little doubt from 

 the researches of Sachs and H. de Vries, that they are 

 due to unequal growth ; but from the reasons already 

 assigned, I cannot believe that this explanation applies 

 to the rapid movements from a delicate touch. 



