LAWS OF RESPONSIVE GROWTH-CURVATURES 



533 



leaflet which is situated in the diametrically opposite line — 

 hitherto horizontal, becomes abruptly vertical (fig. 226). 

 This is the only leaflet which stands out from its fellows, 

 and it is invariably found to be situated on the line diametri- 

 cally opposite to the flower, such differentiation being induced 

 only after flowering. 



All the variations exhibited by diverse forms of response 

 ■ — electrical, mechanical, responsive acceleration or retarda- 

 tion of growth, and growth-curvatures — are only so many 



Fig. 226. Curious Response of Arissema 



Before flowering the leaflets lie in a horizontal plane, as seen in the figure 

 to the left ; but when inflorescence breaks through unilaterally, the 

 • indirect stimulation of the distal side causes erection of the diametrically 

 opposite leaflet, as seen in figure to the right. 



expressions of these two fundamental phenomena, the effects 

 of direct and indirect stimulation. It is these two variables 

 which, conjoined with stimulus unilateral or diffuse, give 

 us all those manifold effects that at first sight would appear 

 to belong to different classes of phenomena. That such a 

 unity does actually underlie them all may be seen at a 

 glance from the following concise statement of responsive 

 effects, induced in pulvini, pulvinoids, and in growing regions 

 which act as pulvinoids. 



