IRRITABILITY TO CONTACT AND TO MECHANICAL SHOCKS 61 



PART III 



MOVEMENTS PRODUCED BY MECHANICAL AND CHEMICAL STIMULI 

 SECTION 14. The Irritability to Contact and to Mechanical Shocks. 



Mechanical agencies, such as pressure, blows, or shaking, produce 

 movements in many cases, including the pronounced variation movements 



FIG. 19. Stem and leaves of Mimosa pudica. The leaf A is fully expanded, whereas the leaf B has been stimu- 

 lated ; p = primary pulvinus, * = secondary pulvini ; the tertiary pulvini at the bases of the leaflets are not shown. 



shown by plants possessing motile pulvini, as in the Papilionaceae, 

 Mimoseae, and Oxalidaceae. (Cf. Figs. 19-24.) The response to stimu- 

 lation is especially rapid in the leaves of Mimosa pudica, and of Desman- 

 thus plenus. The leaves of the first-named plant rapidly pass from the 

 unstimulated (Fig. 19, A) to the stimulated condition (Fig. 19, B) when 



