CHAPTER XX 



GROWTH MOVEMENTS 



ALL plants possess the power of movement to at least a 

 limited extent. The various types of movement and their 

 relations constitute a considerable part of plant physiol- 

 ogy as commonly presented. Here, however, it will be 

 possible merely to outline portions of the subject, which 

 may be further pursued in the special literature. It is 

 entirely beyond the present purpose to consider locomotory 

 movements, likewise the phenomenon of dehiscence, and 

 other effects due to swelling and contraction. Neverthe- 

 less, special movements of turgor are included on account 

 of their closer relationship. 



Movement may occur within the protoplast, and may 

 be limited to the cell, or it may occur in such manner that 

 complex structures exhibit change of position or change 

 in the direction of growth. As popularly regarded, those 

 plants possessing roots are fixed in the soil or other sub- 

 stratum, and movement is only associated with such 

 striking changes as may be seen in the sensitive plant 

 (Mimosapudica),the Venus's-flytrap (Dionaea muscipula), 

 or certain climbers and twiners. As a matter of fact, 

 movement is almost inseparable from growth. 



The elongation of root or shoot is a type of growth 

 movement. There is, furthermore, a remarkable variety 



494 



