202 MIMOSA. [CH. VIII 



(232) Mimosa: movements j^'i^oduced hy stimulation. 



The nature of the movements of Mimosa sensitiva may 

 be seen by giving the plant a shake, when the main 

 petioles will be seen to sink, the second petioles to move 

 together, and the leaflets to close. If the plant is healthy, 

 and is in a moist atmosphere and at a temperature of at 

 least 16° C, the leaves will rapidly recover their former 

 position and may again be irritated. 



An individual leaf may be made to move by gently 

 touching the pulvinus on the under side. Note that a 

 touch on the upper side has no such effect. The period 

 elapsing before the leaf recovers from the effect of the 

 touch varies with the temperature ; thus in one instance 

 a leaf recovered in 8 min. at 23° C. ; in from 12 — 15 min. 

 at 18° C. 



If a lighted match is held beneath a pair of terminal 

 leaflets they close and the passage of the stimulus may be 

 traced by the closmg of pair after pair of leaflets, until it 

 reaches the point where the secondary petioles spring from 

 the main leaf-stalk. The leaflets of the other secondary 

 petioles close one after another in reverse order, i.e. 

 beginning from the base. If the irritation is strong 

 enough the main petiole sinks, and neighbouring leaves 

 may also be affected. 



Lastly, the whole plant may be stimulated by an 

 irritant vapour such as that of ammonia. Place a watch- 

 glass, containing liquor ammonice fo7^tiss., diluted with 

 half its volume of water, near the plant and cover it with 

 a bell-jar. In a few minutes movements indicating 



