174 



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



right induces, as already stated, a right-handed torsion ; that of the second 

 sub-petiole from the right brings about a movement of erection ; the stimula- 

 tion of the third causes a down movement, while that of the extreme left 

 causes a left-handed torsion. The leaf is thus adjusted in space by co-ordinated 

 action of four distinct reflexes. 



(b) Helianthus annuus. 



Results in every way similar are obtained with leaf of Helianthus. Here 

 we can distinguish three main veins or nerves, which collect excitation from 

 different regions of the lamina. 



Experiment 9. — I first tried electric stimulation. The insertions of the 

 electrodes were made in the manner shown in the diagram (fig. 11). 



Experiment 10. — Effect of Discontinuity. — A cut is made between a and b, 

 thus interrupting the continuity of the nerve. Electric stimulation at a 

 induced no responsive movement; stimulation at b induced, however, the 

 normal response by right-handed torsion (lower record fig. 11). 



Experiment 11. — Alternate Electric Stimulation. — The right and left nerve 

 endings in the lamina were stimulated alternately. This gave rise to right- 

 handed and left-handed torsions respectively. In fig. 12, a, is given the record 

 of right-handed torsion. 



The following experiments will show that photic stimulus induces a reaction 

 which is similar to that of electric stimulus : — 



Experiment 12. — Stimulus of Light. — Sunlight was thrown first on the 

 right half and then on the left half of the lamina. The transmitted excita- 

 tions induced corresponding torsional responses (fig. 12, b). A balance was 

 produced when the two halves of the lamina were simultaneously exposed to 

 equal illumination. Here also, as in Mimosa, the heliotropic adjustment is 

 brought about by balanced reactions of the different effectors. 



The movement of a dia-heliotropic lamina has been figuratively compared 

 with the movement of the human eye by which it points itself to a luminous 

 object. It is strange that there is more truth in this comparison than was 

 snspected. In describing the rolling of the eyeball Bayliss says (1) : " When 

 there are two sets of muscles acting on a movable organ, such as the eye or a 

 part of a limb, in such a way that they antagonise one another, it is clear that 

 for effective performance of a particular reflex movement, any contraction of 

 the muscles opposing this movement must be inhibited. Further, the inhibi- 

 tion of one group must proceed pari passu with the excitation of the other 

 group to ensure a well-controlled and steady motion." 



Now, in the torsional adjustment of the leaf due to unequal stimulation of 

 the two receptors — the right and left halves of the lamina — let us take the 



