352 CHAP. XXXI. INXLIXATION AND EXCITATION 



relatively greater excitation at the larger angle may have a 

 physiological significance, to which reference will be presently 

 made. 



Experiment i88. Excitatory reaction at 45°, 60°, and 

 90°. — The excitatory reactions of a different batch of 

 petioles of Tropaeolum were next obtained for the three 

 angles of inclination of 45°, 60°, and 90°. 



Table XXVIII. — Excitatory Reactions at Angles of Inclina- 

 tion OF 45°, 60°, and 90° (Petiole of Tropaeolum). 



Ratio of reactions 

 Ratio of sines 



I : I -28 : I '47 

 I : I -22 : I -41 



The determinations given above again show that the 

 excitation is but approximately proportional to the sine 

 of the angle of inclination, the ratio of reactions at the 

 larger angles being relatively greater. Another series of 

 observations was made, the angle of inclination being 

 increased by steps of 10^. 



Experiment 189. — The photographic records of the 

 reactions at the successive angles of inclination of 45*^, 55°, 

 65^, 75^, and 90^' are reproduced in fig. 207. 



Experiment 190. — Further experiments were carried out 

 with twelve different specimens of the petiole of Tropaeolum 

 and the mean excitatory reaction at the different angles are 

 given in the following table : 



