158 ANIMALS AND PLANTS. [LEOT. 



the nervous system of animals converge towards the 

 conclusion that the nerve fibres, which we have 

 hitherto regarded as ultimate elements of nervous 

 tissue, are not such, but are simply the visible aggrega- 

 tions of vastly more attenuated filaments, the diameter 

 of which dwindles down to the limits of our present 

 microscopic vision, greatly as these have been ex- 

 tended by modern improvements of the microscope ; and 

 that a nerve is, in its essence, nothing but a linear 

 tract of specially modified protoplasm between two 

 points of an organism one of which is able to affect 

 the other by means of the communication so estab- 

 lished. Hence, it is conceivable that even the simplest 

 living being may possess a nervous system. And the 

 question whether plants are provided with a nervous 

 system or not, thus acquires a new aspect, and 

 presents the histologist and physiologist with a 

 problem of extreme difficulty, which must be attacked 

 from a new point of view and by the aid of methods 

 which have yet to be invented. 



Thus it must be admitted that plants may be 

 contractile and locomotive ; that, while locomotive, 

 their movements may have as much appearance of 

 spontaneity as those of the lowest animals ; and that 

 many exhibit actions, comparable to those which are 

 brought about by the agency of a nervous system in 

 animals. And it must be allowed to be possible that 

 further research may reveal the existence of something 

 comparable to a nervous system in plants. So that I 

 know not where we can hope to find any absolute 

 distinction between animals and plants, unless we 



