198 MISCELLANEOUS OBJECTIONS TO THE [Chap. VIL 



It is scarcely possible that the above slight movements, due to 

 a touch or shake, in the young and growing organs of plants, can 

 be of any functional importance to them. But plants possess, in 

 obedience to various stimuli, powers of movement, which are of 

 manifest importance to them ; for instance, towards and more rarely 

 from the light, — in opposition to, and more rarely in the direction 

 of, the attraction of gravity. When the nerves and muscles of an 

 animal are excited by galvanism or by the absorption of strychnine, 

 the consequent movements may be called an incidental result, for 

 the nerves and muscles have not been rendered specially sensitive to 

 these stimuli. So with plants it appears that, from having the 

 power of movement in obedience to certain stimuli, they are excited 

 in an incidental manner by a touch, or by being shaken. Hence 

 there is no great difficulty in admitting that in the case of leaf- 

 climbers and tendril-bearers, it is this tendency which has been 

 taken advantage of and increased through natural selection. It is, 

 however, probable, from reasons which I have assigned in my 

 memoir, that this will have occurred only with plants which had 

 already acquired the power of revolving, and had thus become 

 twiners. 



I have already endeavoured to explain how plants became twiners, 

 namely, by the increase of a tendency to slight and irregular 

 revolving movements, which were at first of no use to them ; this 

 movement, as well as that due to a touch or shake, being the inci- 

 dental result of the power of moving, gained for other and bene- 

 ficial purposes. Whether, during the gradual development of 

 climbing plants, natural selection has been aided by the inherited 

 effects of use, I will not pretend to decide ; but we know that 

 certain periodical movements, for instance the so-called sleep of 

 plants, are governed by habit. 



I have now considered enough, perhaps more than enough, of the 

 cases, selected with care by a skilful naturalist, to prove that natural 

 selection is incompetent to account for the incipient stages of useful 

 structures ; and I have shown, as I hope, that there is no great 

 difficulty on this head. A good opportunity has thus been afforded 

 for enlarging a little on gradations of structure, often associated 

 with changed functions, — an important subject, which was not 

 treated at sufficient length in the former editions of this work. I 

 will now briefly recapitulate the foregoing cases. 



With the giraffe, the continued preservation of the individuals of 

 gome extinct high-reaching ruminant, which had the longest necks,, 

 legs, &c, and could browse a little above the average height, and 



