CLIMBING PLANTS. 
225 
day or two the tendril begins to contract, and ultimately 
assumes the cork-screw-like form represented in the figures. 
It is clear that in spirally contracting the tendril has become 
considerably shorter ; and since the end of the tendril is fixed 
to a branch, it is obvious that the stem of the bryony must be 
dragged nearer to the object which its tendril has caught. 
A. Tendril fully developed, with a young leaf on the opposite side of the stem. 
B. Older tendril, several weeks after its attachment to a wall, with the 
branches thickened and spirally contracted, and with the extremities developed 
into discs. The unattached branches of this tendril have withered and dropped 
off. 
Thus, if a shoot of bryony seizes a support above it, the 
contraction of the tendril will pull up the shoot in the right 
direction. So that in this respect the power of spiral con- 
traction gives a tendril-climber an advantage over leaf-climbers 
which have no contracting power, and therefore no means of 
hauling themselves up to supporting objects. 
But the spiral contraction of tendrils has another use, 
NEW SERIES, VOL. IV. NO. XV. Q 
