22 2 Address to the British Association 



those which occur in muscular contraction. Hardly less 

 noteworthy are the curious methods by which the roots of 

 some plants seek moisture as if by instinct, or those by which 

 the tendrils of certain climbers seek and find appropriate 

 support, and having found it, cling to it by a pseudo-voluntary 

 clasping, or, finally, those by which the little ' Mother-of-a- 

 thousand ' explores surfaces for appropriate hollows in which 

 to deposit her progeny. 



Nevertheless, nothing in the shape of vegetable nervous 

 or muscular tissue has been detected, and as structure and 

 function necessarily vary together, it is impossible to attribute 

 sensations, sense-perceptions, instincts, or voluntary motions 

 to plants, though the principle of individuation in each acts 

 iis in the unfelt psychoses of animals and harmonises its 

 various life processes. 



The conception, then, which commended itself to the 

 clear and certainly unbiased Greek intellect of more than 

 two thousand years ago, that there are three orders of internal 

 organic forces, or principles of individuation, namely, the 

 rational, the animal, and the vegetal,^ appears to me to be 

 justified by the light of the science of our own day. 



I come now to the bearing of these remarks on the science 

 of Biology generally. 



Animals and plants may, as I have before said, be re- 

 garded either statically, by anatomy, or dynamically, by 

 physiology. 



Physiology, as usually understood, regards the properties 



^ Difficult as it confessedly is to draw the dividing line between animals 

 and plants, such difficulty is not inconsistent with the existence of a really 

 profound difference between the two groups. That there should be a radical 

 distinction of nature between two organisms, which distinction our senses, 

 nevertheless, more or less fail to distinguish, is a fact which on any view 

 must be admitted, since animals of very different natures may be indis- 

 tinguishable by us in the germ, and in the earlier stages of their develop- 

 ment. The truth of this is practically supported by the late Mr. Lewes. See 

 the passage quoted ante, vol. i. p. 433. 



