HOW PLANTS CLIMB. 



15 



into a slender hook, for laying hold of anything within reach. In Nepenthes (a 



climbing sort of Pitcher-plant, shown on the right-hand side of the vignette title, 



and one leaf in Fig. 5, on a larger scale), the tip of the — 



blade grows out into a tendril which acts just as does the 



leafstalk of Fig. 4 and of the other leaf-climbers ; at the 



end of this a pitcher, with a lid to it, is generally formed. 



Of this more is to be said hereafter. In that vigorous 



climber, Cobcea, the branching claws and grapples which 



are used to such effect are merely the upper portion of 



a compound leaf changing into tendrils. The tendrils of 



a Pea are similar, but simpler. 



20. Tendril-Climbers are best illustrated by such plants 

 as Passion-flowers (see vignette title, on the left, and Fig. 

 6) : here the tendril is a simple thread-like shoot, for the - 

 purpose of climbing and nothing else. This is the most 

 exquisite, and under many circumstances the most advan- 

 tageous, as it is one of the commonest of the contrivances 

 for climbing. The tendril, as it grows, stretches out v. ^'«- ^- ^"^ "*' ''^i'™"'''- 

 horizontally, as if in search of a supporting object. More slender than a stem 

 or any other sort of stalk, it can thus extend farther at the least expense of 

 material. 



21. In the most perfect tendrils, and notably in the slender Passion-flowers 

 (such as the annual Fassiflora gracilis, and the Maple-leaved species, P. acerifolia, 

 Fig. 6), opportunities for securing a hold are much increased by the revolving of 

 the tendril. It sweeps circuits, like the stem of a twiner, although with less reg- 

 ularity, sometimes, however, with greater rapidity. In hot weather these tendrils 

 often move through the complete circle in an hour or less, or even so fast that 

 the motion of the end of a long tendril may sometimes be distinctly seen in a 

 part of its course. The revolving of tendrils is more fitful than that of twining 

 stems : they often stop for a while, or move very slowly or irregularly. Some 

 tendrils, as we shall soon see, do not revolve at all. 



22. If a tendril does not reach anything, after attaining its full growth and - 

 remaining for some time outstretched, it then either coils up from the end (as 

 seen in the middle tendril of Fig. 6), or else becomes flabby, hangs down in an 

 exhausted state, dies, and withers away. 



