Cuar. V. CONCLUDING REMARKS. 189 
Concluding Remarks on Climbing Plants. 
Plants become climbers, in order, as it may be 
presumed, to reach the light, and to expose a large 
surface of their leaves to its action and to that of the 
free air. This is effected by climbers with wonderfully 
little expenditure of organized matter, in comparison 
with trees, which have to support a load of heavy 
branches by a massive trunk. Hence, no doubt, it 
arises that there are so many climbing plants in all 
quarters of the world, belonging to so many different 
orders. These plants have been arranged under four 
classes, disregarding those which merely scramble over 
bushes without any special aid. Hook-climbers are 
the least efficient of all, at least in our temperate 
countries, and can climb only in the midst of an 
entangled mass of vegetation. Root-climbers are 
excellently adapted to ascend naked faces of rock 
or trunks of trees; when, however, they climb trunks 
they are compelled to keep much in the shade; 
they cannot pass from branch to branch and thus cover 
the whole summit of a tree, for their rootlets require 
long-continued and close contact with a steady surface 
in order to adhere. The two great classes of twiners 
and of plants with sensitive organs, namely, leaf- 
climbers and tendril-bearers taken together, far exceed 
in number and in the perfection of their mechanism the 
_ climbers of the two first classes. Those which have 
the power of spontaneously revolving and of grasping 
objects with which they come in contact, easily pass 
