GROWTH AND MOVEMENT 



135 



cells, and it is structurally impossible that their mechanical effects 

 should exceed, as they mostly fall short of, the limit of the pressure 

 of the protoplast upon the containing walls. Such movements of 

 the plant-body are brought about in an essentially different way from 

 those positive contractions of muscle-fibres, which are the source of 

 movement in the animal body. In this, as in so many other features, 

 the two kingdoms show evidence of their initial divergence. However 

 parallel their behaviour may appear to be, when fully analysed it 

 becomes apparent that it is analogy, rather than any closer correspon- 

 dence, that holds between them. For we do not find that either 

 contractile muscular fibres, or a specialised nerve-system exist in 

 the body of the Plant. Such movements as Plants show, and even 

 the conveyance of stimuli, are brought about without them. 



