192 CONCLUDING REMARKS. Cuar. 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 Tropzolum, 
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- 
