360 BOTANY PART i 



The leaves of this plant are doubly compound (Fig. 291). The 

 four secondary leaf - stalks, to which closely crowded leaflets are 

 attached left and right, are articulated by well-developed pulvini with 

 the primary leaf-stalks ; while they, in turn, as well as the leaflets, 

 are similarly provided with motile organs. Thus all these different 

 parts are capable of independent movement, and the appearance of 

 the entire leaf becomes, in consequence, greatly modified. In their 

 unirritated, light position (Fig. 291, on the left) the leaf -stalk is 

 directed obliquely upwards, while the secondary petioles with their 

 leaflets are extended almost" in one plane. Upon any vibration of 



FIG. 291. Mimosa pudica, with leaves in normal, diurnal position ; to the right, in the position 

 assumed on stimulation ; B, inflorescences. 



the leaf, in favourable conditions of temperature (25-30 C.) and 

 moisture, all its parts perform rapid movements. The leaflets fold 

 together, and, at the same time, move forward, the secondary petioles 

 lay themselves laterally together, while the primary leaf-stalk sinks 

 downwards (Fig. 291, on the right). Leaves thus affected, if left 

 undisturbed, soon resume their former position. 



The behaviour of the leaves is still more remarkable when only a 

 few of the leaflets are acted upon by the stimulus. This is easily 

 demonstrated by holding a burning match near the leaflets of one of 

 the pinnae. The leaflets directly affected by the flame fold quickly 

 upwards, and this movement is performed successively by each pair of 

 leaflets of the pinna until the articulation with the primary leaf- 

 stalk is reached. The stimulation is then conveyed to the other 

 pinnae, the leaflets of which go through the same movement in the 



