108 TENDRIL-BEARERS. Cuar. II. 
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 climbing- 
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 space 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 
all power of movement, and contracts spirally into an 
entangled mass. Although the tendrils revolve with 
unusual rapidity, the movement lasts for only a short 
