108 TENDRIL-BE AEERS. Chap. III. 



begins after an unusually short interval of time, 

 namely, in about twelve hours. 



Before the tendril is mature, the terminal branchlets 

 cohere, and the hooks are curled closely inwards. At 

 this period no part is sensitive to a touch ; but as soon 

 as the branches diverge and the hooks stand out, full 

 sensitiveness is acquired. It is a singular circumstance 

 that immature tendrils revolve at their full velocity 

 before they become sensitive, but in a useless manner, 

 as in this state they can catch nothing. This want 

 of perfect co-adaptation, though only for a short time, 

 between the structure and the functions of a climbino:- 

 plant is a rare event. A tendril, as soon as it is ready 

 to act, stands, together with the supporting petiole, 

 vertically upwards. The leaflets borne by the petiole 

 are at this time quite small, and the extremity of the 

 growing stem is bent to one side so as to be out 

 of the way of the revolving tendril, which sweeps 

 large circles directly over head. The tendrils thus 

 revolve in a position well adapted for catching objects 

 standing above ; and by this means the ascent of the 

 plant is favoured. If no object is caught, the leaf 

 with its tendril bends downwards and ultimately 

 assumes a horizontal position. An open sj)ace is 

 thus left for the next succeeding and younger tendril 

 .to stand vertically upwards and to revolve freely. 

 As soon as an old tendril bends downwards, it loses 

 ail power of movement, and contracts spirally into an 

 entangled mass. Although the tendrils revolve with 

 unusual rapidity, the movement lasts for only a short 



