58 LIVING PLANTS 



will cause reactions. If the movement of the 

 air is continuous and freshens to a breeze, or 

 the drops of water are followed by a steady 

 rain, the plant finalh' replaces the pinnules in 

 the original position, though blown about or 

 beaten by the rain . The plant is enabled to do 

 this by its great power of accommodation to 

 any force acting upon it. The real stimulus 

 is not the force in itself but consists in changes 

 in the forces acting upon the plant. This may 

 be demonstrated if a specimen is subjected to 

 a spray of water forming an artificial rain- 

 Repetition storm in a greenhouse. After a time it be- 

 of stimuli comes accustomed to the falling water and 

 resumes the normal position. If now the 

 force of the spray is suddenly increased, a re- 

 action is shown, and the pinnules are closed. 

 After exposure to the heavier spray for a time 

 it once more resumes the normal attitude and 

 the experiment may be repeated with similar 

 results. A specimen of mimosa grown in a 

 pot may be carried on a journey in a wagon 

 or railroad train, and may be seen to resume 

 the normal position after it has become accus- 

 tomed to the jarring from the vehicle, if the 

 temperature and light are favorable. While 

 an individual may thus accommodate itself 

 to an unusual intensity of any force, it is as 

 delicately sensitive to other stimuli as usual. 

 Thus one may stand some distance from a 



