1 92 CONCLUDING REMARKS. Chap. V. 



bearers ? Of what advantage has this been to them ? 

 Why did they not remain simple twiners ? We can 

 see several reasons. It might be an advantage to a 

 plant to acquire a thicker stem, with short internodes 

 bearing many or large leaves ; and such stems are ill 

 fitted for twining. Any one who will look during 

 windy weather at twining plants will see that they are 

 easily blown from their support ; not so with tendril- 

 bearers or leaf-climbers, for they quickly and firmly 

 grasp their support by a much more efficient kind of 

 movement. In those plants which still twine, but at 

 the same time possess tendrils or sensitive petioles, as 

 some species of Bignonia, Clematis, and Tropaaolum, 

 it can readily be observed how incomparably better 

 they grasp an upright stick than do simple twiners. 

 Tendrils, from possessing this power of grasping 

 an object, can be made long and thin ; so that 

 little organic matter is expended in their develop- 

 ment, and yet they sweep a wide circle in search 

 of a support. Tendril-bearers can, from their first 

 growth, ascend along the outer branches of any neigh- 

 bouring bush, and they are thus always fully exposed 

 to the light ; twiners, on the contrary, are best fitted 

 to ascend bare stems, and generally have to start in 

 the shade. Within tall and dense tropical forests, 

 twining plants would probably succeed better than 

 most kinds of tendril-bearers ; but the majority of 

 twiners, at least in our temperate regions, from the 

 nature of their revolving movement, cannot ascend 

 thick trunks, whereas this can be affected by tendril- 



