CHAP. IV Movement and Nervous Action in Plants 6 1 



straggling branches of their neighbours, or twine them- 

 selves around the upright stems, or moor themselves by 

 sensitive elastic tendrils to the twigs of their bearers ; thus 

 reaching out of the crowded life of the ground herbage, or 

 out of the darkness and closeness of the jungle, to room 

 and fresh air and sunlight above, 



Darwin arranged these climbers in four grades. Rising 

 a little above the crowd of those which merely scramble 

 over surrounding bushes, there are the hook -climbers, 

 such as Jack-run-the-hedge {Galium Apariiie\ and root- 

 climbers, such as the Ivy. More efficient are the twiners, 

 like the Hop {Humulus) and the Honeysuckle {Lonicera)^ 

 but the climbing habit is most frequently and most 

 perfectly exhibited by plants with sensitive prehensile 

 organs, either leaves or tendrils. 



Let us consider these different kinds of climbers more 

 precisely, recognising, however, that the classification is 

 merely one of general convenience, for there are gradations 

 between scramblers and hook-climbers, between creeping 

 plants and root-climbers, between those which climb by 

 their leaves and the tendril-bearers. 



The hook-climbers are least effective, being little more 

 than scramblers well equipped with hooks which are caught 

 up in the surrounding vegetation. Thus many brambles 

 and roses are merely scramblers, while the New Zealand 

 Rubus squarrostcs and a rose known as Rosa setigera may 

 be fairly called climbers. The habit is very well illustrated 

 by those oriental palms which are often called Rotangs 

 {e.g. Calanms extenst(s), which with barbed branches in- 

 sinuate themselves and grow up through their more 

 vigorous neighbours. A more familiar example is the 

 Jack-run-the-hedge, whose stem and leaves are beset with 

 backward-directed hooks most efficient in binding the plant 

 to the growth of the hedgerow. 



