204 CONCLUDING REMARKS. Cuar. 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. 
