TENDRIL-BEARERS. 101 



to prolonged contact. Hence we see that the sensitiveness of ten- 

 drils is a special and localized capacity, quite independent of the 

 power of spontaneously moving ; for the curling of the terminal 

 portion from a touch does not in the least interrupt the sponta- 

 neous revolving movement of the lower part. In Bignonia unguis 

 and its close allies the petioles of the leaves, as well as the ten- 

 drils, are sensitive to a touch. 



Twining plants when they come into contact with a stick, curl 

 round it invariably in the direction of their revolving movement ; 

 but tendrils curl indifferently to either side, in accordance with 

 the position of the stick aud the side which is first touched. The 

 clasping-movement of the extremity apparently is not steady, but 

 vermicular in its nature, as may be inferred from the manner m 

 which the tendrils of the Echinoci/slis slowly crawled round a 

 smooth stick. 



As with a few exceptions tendrils spontaneously revolve, it may 

 be asked, Why are they endowed with sensitiveness ?— why, when 

 they come into contact with a stick, do they not, like a twining 

 plant, spirally wind round it? One reason may be that in most 

 cases they are so flexible and thin that, when brought into contact 

 with a stick, they would yield, and their revolving movement 

 would not be arrested ; they would thus be dragged onwards and 

 away from the stick. Moreover the sensitive extremities have no 

 revolving power, and could not by this means curl round any 

 object. With twining plants, on the other hand, the extremity 

 of the shoot spontaneously bends more than any other part ; and 

 this is of high importance to the ascending power of the plant, as 

 may be seen on a windy day. It is, however, possible that the slow 

 movement of the basal and stifter parts of certain tendrils, which 

 wind round sticks placed in their course, may be analogous to that 

 of twining plants. I doubt this; but I hardly attended suffi- 

 ciently to this point, and it would be difficult to distinguish 

 between a movement due to extremely dull sensitiveness and that 

 resulting from the arrestment of the lower part together with 

 the continued movement of the terminal part of a tendril. 



Tendrils which are only three-fourths grown, and perhaps 

 even when younger, but not whilst extremely young, have the 

 power of revolving and of grasping any object which they may 

 touch. These two capacities generally commence at about the 

 same period, and tail when the tendril is full grown. But in 

 the Cobcea and Passijlora punctata the tendrils began revolving 

 in a quite useless manner, before they became sensitive. In 



