CLIMBING PLANTS 33 



The rootlets of the Ivy and other cUinbers of tlie same habit 

 always avoid the Ught ; and if they are not originally formed on 

 the side of the stem facing the supporting surface, they soon turn 

 towards the latter, and give rise to httle clinging suckers that 

 firmly adhere. If they come in contact with a bare rock, or with 

 a surface from which no nutriment can be derived, they serve the 

 one puri)ose of clinging only ; but if they reach even a small amount 

 of nutritive soil, they produce absorbent fibres that are capable 

 of extracting food. 



The ivy usually clings to the bark of trees or to old walls, the 

 crevices of which often contain some small amount of transported 

 soil, or more or less organic soil formed by the growth and decay of 

 low forms of vegetable fife ; and thus the tree is enabled to obtain 

 a little food from the objects that give it the necessary mechanical 

 support. 



The well-known Virginian Creeper [Ampelopsis) produces rootlets 

 by means of which it can cling to very smooth surfaces. Its light- 

 avoiding ' tendrils ' always turn to the wall or other supporting 

 body ; and, on coming in contact with it, give off little branches 

 wliich diverge Uke the toes of the tree-frog, and produce little 

 adhesive discs which hold on firmly Ijy the aid of a sticky secretion. 

 Perhaps the most interesting of all cHmbing plants are those 

 which twine their stems around the jjrops afforded by the neigh- 

 bouring growths. As before stated, the stems of these plants 

 are erect when very young ; but after they have reached a certain 

 height the top of the stem bends to one side, and then, as the growth 

 proceeds, it turns slowly round and round, desci'ibing a circle in 

 the horizontal plane, thus seeking some support round which it 

 can t^\dne. 



The rate at which the top of the stem revolves varies in different 

 plants, and also in the same plant according to the temperature 

 and other conditions affecting the growth. In some species the 

 upper portion describes a complete cii'cle in less than two hours 

 during warm weather, while in others a single revolution may 

 occupy one or two days. 



It will be seen, from the natiu-e of these movements, that the 

 revolving stem is far more Ukely to come in contact with erect, 

 rather than with horizontal supports, and observations made on 

 twining stems will show that they seldom fix themselves round 

 supports which are placed horizontally or only on a slight inchnc. 

 In fact, some of these stems seem qaite unable to twist themselves 



D 



