JULY 163 



contact with a twig, a cord, or a wire, it wraps its stalk 

 so firmly round it that, when a few days later the 

 tissues have hardened, it is impossible to unclasp it 

 without a fracture. 



The action of tendril-climbers may be conveniently 

 studied in the common garden pea,^ in which the leaf- 

 stalk is produced beyond the leaf in the form of a wiry, 

 sensitive organ — a feeler like a green thread two inches 

 long, or more. While the main stem of the plant 

 revolves spirally on its own axis in its upward growth, 

 the tendril moves independently, waving in circles or, 

 to be accurate, in ellipses. Darwin watched a tendril 

 of the common pea and found that it described a 

 complete ellipse in one hour and thirty minutes. This 

 double movement of stem and tendril is pretty sure to 

 bring the latter into contact with some form of support, 

 whereupon the tendril immediately wraps itself firmly 

 round it. 



The most familiar type of British root-climber is the 

 common ivy, which is able to emit what are called 

 aerial roots along the whole length of its stem and 

 branches, thereby clinging closely to a wall or tree 

 and rising to an indefinite height. The precise action 

 of these rootlets is not, I believe, thoroughly under- 

 stood. Experiments with the creeping fig (Ficua 

 repens), often cultivated in greenhouses, proved that 



1 I never write the word 'pea' without a mental apology, for- 

 asmuch as, rightly speaking, there is no such English word. In 

 Middle English the plant was jpese, and its seed was expressed by the 

 plural peaen. But we have come to talk glibly of ' a pea, ' just as we 

 talk of ' a cherry,' through our ancestors, when they borrowed the 

 French word cerise, believing it to be a plural form. 



