130 



BOTANY OF THE LIVING PLANT 



the hinge is raised: if it is greater on the upper side the hinge is 

 depressed. This appears to be the mechanism of the so-called 

 " Sleep-Movements " of the Leguminosae, Wood-Sorrel, and various 

 other plants. 



But the point which gives the Sensitive Plant its name is that it 

 also executes movements of a like nature in response to mechanical shock. 

 The disturbance of walking roughly through a patch of Mimosa pudica 

 leaves a broad track of completely transformed vegetation. But if 

 the stimulus be applied gently, steps in the change can be observed. 



Fig. 90. 



Shoot of Mimosa pudica. I. with leaves in the normal day-position. II. in the 

 night-position assumed at dusk, or after stimulation. B= inflorescences. (After 

 Strasburger.) 



A gentle touch at the sensitive lower surface of the hinge at the base 

 of the petiole makes the whole leaf fall, and the stimulus may then be 

 extended outwards to the pinnae and successive pinnules. Or if the 

 distal pair of pinnules be pinched, or stimulated with the hot head of 

 an extinguished match, the stimulus received distally will extend 

 downwards. The pinnules will fold in successive pairs, and finally 

 the leaf as a whole will fall. If the stimulus be strong it may extend 

 along the stem to other leaves. There may thus be a conveyance of 

 the stimulus to a distance. 



The movement following on shock is in the first instance due to 

 stimulus of the protoplasts of the turgid cells, resulting in their loss 





