RESPONSE OF GROWING ORGANS 



113 



pulvinus of Desmodium, at the angles of 45° and 90°. The 



record (fig. 61) shows that the phototropic effect increases 



with the directive angle. In the present case the ratio of 



the two effects is i-6 : i, which is not very different from 



^, ^. sin 90° 

 the ratio —. — ^-5 = i •4. 

 sm 45° ^ 



Experiment 67. Response of growing organs. — A parallel 



experiment was carried out with the flower-bud of Crinum 



Fig. 61, 



Fig. 62. 



Fig. 61. Effect of angle of incidence of light on tropic curvature 



of pulvinus of Desmodium. 

 The first response is to light at 45°, and the second at 90°. 



Fig. 62. Records of tropic curvature of growing bud of Crinum 

 on alternate stimulation by light at 45° and at 90°. 



held vertical. Unilateral light was applied alternately at 

 45° and 90° in two successive series. It may be said in 

 general that the excitability of a tissue in a condition slightly 

 below par is increased by previous stimulation. From the 

 series of responses obtained under alternate stimulation at 

 45° and at 90° it is possible to ascertain whether any varia- 

 tion of excitability had occurred during the course of the 

 experiment, in order to make allowance for it. The records 

 show that stimulation did enhance the excitability of the 

 organ to a small extent. Thus the first stimulation at 45° 



