172 ANIMALS AND PLANTS vi 



have hitherto regarded as ultimate elements of 

 nervous tissue, are not such, but are simply the 

 visible aggregations of vastly more attenuated 

 filaments, the diameter of which dwindles down to 

 the limits of our present microscopic vision, greatly 

 as these have been extended by modern improve- 

 ments 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 established. 

 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 



