CLIMBING PLANTS. 
223 
from it, and thus easily find out where the wall lies, up which 
they have to climb. A tendril which has come against the wall 
is often seen to rise and come down afresh, as if not satisfied 
with its first position. In a few days after a tendril has 
touched a wall the tip swells up, becomes red, and forms one of 
the little feet or sticky cushions by which the tendrils adhere, 
and which are shown in Fig. 5. The adherence is caused by a 
resinous cement secreted by the cushions, and which forms a 
strong bond of union between the wall and the tendril. After 
the tendril has become attached it becomes woody, and is in 
this state remarkably durable, and may remain firmly attached 
and quite strong, for as many as fifteen years. 
Besides this sense of touch, by which a Bignonia tendril 
distinguishes between the objects which it touches, there are 
other instances of much more perfect and incomprehensible 
sensibility. Thus some tendrils, which are so sensitive that 
they curl up when a weight of —th or even -gVth grain is 
placed on them, do not take the least notice of a shower of rain 
whose falling drops must cause a much greater shock to the 
tendrils. 
Again, some tendrils seem to have the power of distinguish- 
ing between objects which they wish to seize, and their brother 
tendrils which they do not wish to catch. A tendril may be 
drawn repeatedly over another without causing the latter to 
contract. 
The tendrils of another excellent climber, Cobcea scanclens, 
possess some curious properties. The tendrils are much divided, 
and end in delicate branchlets, as thin as bristles, and very 
flexible, each bearing a minute double hook at its tip. These 
are formed of a hard, woody substance, and are as sharp as 
needles ; a single tendril may bear between ninety and a 
hundred of these beautiful little grappling-hooks. The flexi- 
bility of the tendrils is of service in allowing them to be blown 
about by a breath of wind, and they can thus be made to seize 
hold of objects which are out of reach of the ordinary revolv- 
ing movements. Many tendrils can only seize a stick by 
curling round it, and this even in the most sensitive tendril 
must take a minute or two ; but with Cobaea, the sharp hooks 
catch hold of little irregularities on the bark the moment the 
tendril comes into contact with it, and afterwards the tendril 
can curl round and make the attachment permanent. The im- 
portance of this power of temporary attachment is shown by 
placing a glass rod near a Cobaea plant. Under these conditions 
the tendrils always fail to get hold of the glass, on which its 
grapple-like hooks cannot seize. 
The movement of the little hook-bearing branches is very 
remarkable in this species. If a tendril catches an object with 
