248 MOVEMENT IN PLANTS. 



their normal position while the shaking is continued, but 

 in 5 to 15 minutes after the shaking has stopped the leaves 

 become sensitive again. 



344. Sensitiveness of Lower Side of Fulvinus. 



With a pencil or thin stick tap or rub the upper surface 

 of the large pulvinus at the base of the petiole : at first 

 there is no response, even to vigorous stimulation, but if 

 it is continued a response is eventually obtained. Now 

 gently tap or rub the lower side of the pulvinus : an im- 

 mediate response is made to even a slight stimulus. 



345. Effect of Repeated Stimuli. With a light piece 

 of wood strike the lower side of the main pulvinus re- 

 peatedly, at intervals of half a minute for about 5 minutes. 

 On leaving the plant to itself the leaf rises, but at first it 

 does not respond to a stimulus, though it soon regains its 

 irritability. If the blows are applied more frequently 

 about ten per minute the stalk falls at first but after- 

 wards rises (in spite of the continued blows) and is then 

 insensible even to stronger stimuli for some time. 



346. Heat as a Stimulus. Hold a lighted match 

 below the tip of one of the four secondary stalks, and note 

 the successive closing of the leaflets of this stalk ; then the 

 stimulus travels in the opposite direction from the bases 

 of the other three secondary stalks towards their tips ; 

 finally the main stalk sinks, and if the stimulus is con- 

 tinued the neighbouring leaves are also affected. 



347. Irritant vapours, like ammonia, act as a stimulus 

 on Mimosa leaves. Set a plant under a bell-glass, along 

 with a watch-glass containing a little ammonia. Note 

 the movements of the leaves, and after a few minutes 

 remove the bell-glass and the ammonia, to prevent the 

 latter from injuring the plant. 



348. Effects of Anaesthetics. The leaves of Mimosa 

 are rendered insensible by chloroform and other anaesthe- 

 tics. Stimulate a leaf so that the leaflets close up, then 



