102 METHODS OF CLIMBING [CH. 



Climbing is accomplished in several ways, but the 

 principles in play are of two kinds. Either the shoot- 

 axis itself is the active agent in obtaining the support 

 required, as in a Bramble which scrambles over a hedge, 

 or a Hop which twines up a pole ; or the shoot-axis is, on 

 the whole, passively supported by appendages which cling 

 to the wall, trunk, twigs, or other objects up which the 

 climbing is effected, as in the Ivy clinging by roots (Fig. 48), 

 or the Pea or Vine (Fig. 49) which climb by means of 

 tendrils. Indeed the above gives an outline scheme for 

 treating the subject, for although a few plants employ 

 simultaneously two or more of the above means, most 

 adopt one only. 



With regard to plants which climb by means of 

 anchoring rootlets, the Ivy is a good example to begin 

 with. 



Its young shoots, at first erect and independent, apply 

 themselves close to the wall, or similar support, owing to 

 negative heliotropism, and put out short rootlets at first 

 from the neighbourhood of the nodes, and later along the 

 internodes, on the side of the stem which is next the wall 

 and therefore darkest and most sheltered. These rootlets 

 fit their surfaces closely into the roughnesses of the wall, 

 crevices and so forth, and glue themselves there by the 

 softening of their cells. 



Some species of Figs (e.g. Ficus repens) can cling by 

 similar roots even to the glass of a greenhouse, where 

 Darwin observed them exude a sticky fluid, which soon 

 cemented them tightly to the glass. 



Piper flumense, Tecoma radicans, several species of 

 Cereus, Marcgravia, and various Aroidea3 also climb by 

 means of anchoring roots like the Ivy. Other cases are 

 Ercilla, the stem of which creeps up a wall and is 

 anchored there by adhesive discs which are roots, and 



