174 TENDKIL-BEAKEES. Ciui'. IV. 



with a stick, do they not, like twining plants, spirally 

 wind round it ? One reason may be that they are in 

 most cases so flexible and thin, that when brought 

 into contact with any object, they would almost 

 certainly yield and be dragged onwards by the revolv- 

 ing movement. Moreover, the sensitive extremities 

 have no revolving power as far as I have observed, 

 and could not by this means curl round a support. 

 With twining plants, on the other hand, the extremity 

 spontaneously bends more than any other part; and 

 this is of high importance for the ascent of the plant, 

 as may be seen on a windy day. It is, however, possible 

 that the slow movement of ihe basal and stiffer parts 

 of certain tendrils, which wind round sticks placed in 

 their path, may be analogous to that of twining plants. 

 But I hardly attended sufficiently to this point, and it 

 would have been difficult to distinguish between a 

 movement due to extremely dull irritability, from the 

 arrestment of the lower part, whilst the upper pai't 

 continued to move onwards. 



Tendrils which are only three-fourths grown, and 

 perhaps even at an earlier age, but not whilst extremely 

 young, have the power of revolving and of grasping 

 any object which they touch. These two capacities 

 are generally acquired at about the same period, and 

 both fail when the tendril is full grown. But in 

 Cohasa and Passiflora punctata the tendrils begin to 

 revolve in a useless manner, before they have become 

 sensitive. In the Echinocystis they retain their 

 sensitiveness for some time after they have ceased to 



