TUTiBRTL-BEABEiaS. 101 



to prolonged contact. Hence we see that tlie 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 ; 

 hut tendrils curl indifferently to either side, ia accordance with 

 the position of the stick and 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 in 

 which the tendrils of the Echinocystis slowly crawled round a 

 smooth stick. 



As with a few exceptions tendrils spontaneously revolve, it may 



Why 



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 

 revoMng 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 tbe ascending power of the plant, as 

 may be seen on a windy day. It isjhowever^possible that the slow 

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

 wind round sticks placed in their course, maybe 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 fail when the tendril is full grown. But in 



Passijlora punctata the tendrils began 



manner 



In 



