CH. VIIl] MIMOSA. 187 



If a lighted match is held beneath a pair of termiual 

 leaflets they close and the passage of the stimulus may be 

 traced by the closing of leaflet after leaflet, 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 fortiss, diluted with 

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

 a bell-jar. In a few minutes movements indicating 

 stimulation begin in the leaves nearest the watch-glass: 

 the bell should be then removed, as the plant is easily 

 injured by ammonia. 



(234) Mimosa: temperature. 



On the bottom of a glass cylinder place a layer of wet 

 sawdust in which a small Mimosa growing in a pot may 

 be sunk ; the cylinder is to be placed in a large inverted 

 bell-jar filled with water of which the temperature can be 

 varied by ice or by hot water as the case may be. The 

 cylinder must be covered with a glass plate through 

 a hole in which it is possible to touch the plant 

 so as to test its sensitiveness. Assuming that the 

 temperature in the cylinder is about 20° C. and that the 

 plant is in an irritable condition, it is best to begin by 

 adding ice so that the temperature in the cylinder may 



