24 STRUCTURE AND PROPERTIES 



branch, we shall find that its cuticle stretches 

 during a considerable period, after which it 

 breaks, and is replaced by an epidermis : the 

 same thing occurs in all cases in which we can 

 follow the growth of any organ ; and if plants 

 appear to increase indefinitely, it is because fresh 

 organs are perpetually added to the former ones, 

 and the older parts fall sooner or later into that 

 inert state in which they are no longer capable 

 of extension. 



18. Elasticity of vegetable tissue is that pro- 

 perty by which each membrane is enabled to 

 resume its proper position when deranged by any 

 external force. It implies a certain degree of 

 rigidity, and is consequently less sensible when 

 the tissue, having received but few deposits, is 

 still in a semi-fluid state, than when it is of older 

 growth. This property is worthy of remark, 

 because it occasions certain movements, which 

 might be mistaken for vital action. It is very 

 variable in intensity. Every one must have ob- 

 served that a branch, if bent out of its natural 

 course, returns to it of itself ; but in certain cases 

 this is not so the dracocephalum-moldavicum 

 has pedicels which may be turned from their 

 natural direction, and will remain in that which 

 has been forced on them. The plant, on account 



