CONCLUDING ItEMAltKS. 117 



Fifthly, we have in the tendrils, whatever their homological 

 nature may be, in the petioles and tips of the leaves of leaf- 

 climbers, in the stem in one case, and apparently in the aerial 

 roots of the Vanilla, movements — often rapid movements — from 

 contact with any body. Extremely slight pressure suffices to cause 

 the movement. These several organs, after bendiug from a touch, 

 become straight again, and again bend when touched. 



Sixthly, and lastly, most tendrils, soon after clasping a support, 

 but not after a mere temporary curvature, contract spirally. The 

 stimulus from the act of clasping some object seems to travel 

 slowly down the whole length of the tendril. Many tendrils, 

 moreover, ultimately contract spontaneously even if they have 

 caught no object ; but this latter useless movement occurs only 

 after a considerable lapse of time. 



"We have seen how diversified arc the movements of climbing 

 plants. These plants are numerous enough to form a conspicuous 

 feature in the vegetable kingdom ; every one has heard that this 

 is the case in tropical forests ; but even in the thickets of our 

 temperate regions the number of kinds and of individual plants is 

 considerable, as will be found by counting them. They belong to 

 many and widely different orders. To gain some crude idea of 

 their distribution in the vegetable series, I marked, from the lists 

 given by Mohl and Palm (adding a few myself, and a competent 

 botanist, no doubt, could add many more), all those families in 

 ' Lindley's Vegetable Kingdom ' which include plants in any of 

 our several subdivisions of twiners, leaf-climbers, and tendril- 

 bearers; and these (at least, some in each group) all have the 

 power of spontaneously revolving. Lindley divides Phanerogamic 

 plants into fifty -nine Alliances ; of these, no less than above half, 

 namely thirty-five, include climbing plants according to the above 

 definition, hook- and root-climbers being excluded. To these a 

 few Cryptogamic plants must be added which climb by revolving. 

 "When 'we reflect on this wide serial distribution of plants having 

 this power, and when we know that in some of the largest, well- 

 defined orders, such as the Composite, Kubiacea\ Scrophulari- 

 ace», Liliace», &c, two or three genera alone, out of the host of 

 genera in each, have this power, the conclusion is forced on our 

 minds that the capacity of acquiring the revolving-power on which 

 most climbers depend is inherent, though undeveloped, in almost 

 every plant in the vegetable kingdom. 



It has often been vaguely asserted that plants are distinguished 

 from animals by not having the power of movement. It should rather 



