172 



Sir J. C. Bose and Mr. S. 0. Guha. 



Experiment 7. — The left sub-petiole was now stimulated by feeble 

 tetanising shock, as in the last experiment. The response was now by a 

 left-handed torsion (fig. 10, a) ; the nervous impulse now reached the left 

 flank of the pulvinus, or the left-effector, the characteristic response of 

 which is by a left-handed torsion. The leaf may thus be twisted to the 

 right or to the left by alternate stimulation of the two sub-petioles. A 

 feeble tetanising shock should be used for these experiments, since a strong- 

 excitation becomes diffused as it reaches the fibro-vascular ring in the 

 pulvinus, and the predominant excitation of the entire lower half would 

 then mask the characteristic effects of the right or the left effectors. As 







.' ,4. ... \ - 



R . 







R \. 









\ 





t 



a 



L 





b 



L 



Fig. 10. — Responsive torsion by transmitted excitation in Mimosa under (a), electric 

 stimulus ; (b), under stimulus of light. Note iight-handedand left-handed torsions 

 by stimulation of the right and left sub-petioles. Successive dots in (a) are at 

 intervals of 2 seconds, and in (b) 20 seconds. Note the quick reaction under electric, 

 and slower reaction under photic stimulation. 



regards leaves with four sub-petioles, we shall presently find that they 

 transmit definite impulses to the four quadrants of the pulvinus, to the right 

 and to the left, to the upper and the lower effectors, thus giving rise to 

 definite reflexes. 



Experiment 8. — Stimulus of Light. — I next tried the action of stimulus of 

 light on the leaflets of the right sub-petiole ; here also the transmitted 

 excitation induced a right-handed torsion. The latent period was, for 

 reasons explained before, longer than in the case of electric stimulation. 

 It should be remembered that the light was applied vertically, and the 

 responsive torsion was such that the amount of light absorbed by the 



