170 



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



plotted from the mean values given in Table I, illustrates this in a striking 

 manner. 



IV. The Transmitted Nervous Impulse. 



In certain experiments with petioles having four bundles, I allowed the 

 probe to pass vertically through the petiole when it encountered the upper 

 and lower bundles. I thus obtained maximum transmitted excitations in the 

 phloems of the upper fibro-vascular bundle, and a similar maximum in the 

 phloems of the lower bundle, the intervening layers of tissue being practically 

 non-conducting. From this it follows that excitatory impulse is propagated 

 along definite channels through the length of the petiole. 



8. Definite Innervation. 



"We shall now follow the nervous strand from the perceptive lamina to the 

 motor organ. In Mimosa, the leaflets attached to the sub-petioles form the 

 perceptive area for light. The excitation is conducted along the phloem 

 strand of the sub-petiole, and thence through the connected phloem in the 

 petiole. In leaves with four sub-petioles there are, as stated before, four 

 main bundles which reach the motile organ, the pulvinus. There the fibro- 

 vascular bundles apparently fuse, but very fine section of the pulvinus shows 

 lines of separation. In any case, I shall be able to show that nervous strands 

 are physiologically distinct. These terminate in the four effectors, of which 

 two are lateral, the right and the left effectors; the other two are upper and 

 lower effectors. In younger specimens of Mimosa there are two sub-petioles 

 instead of four, and the two nerve strands are continued to the right and 

 left flanks of the pulvinus, the particular innervation being to the right and 

 left effectors respectively. In Helianthus, the right and left nerve pass along 

 the right and left flank of the petiole, which, as we have seen, serves as an 

 extended motor organ. The following results will show that these strands 

 function as distinct nerves : — 



Experiment 4. — One electrode was pricked in so as to make contact with 

 the phloem of the right bundle embedded in the petiole ; the second contact 

 was made with a distant indifferent point. Electric stimulation of the 

 right vein of the lamina of Helianthus gave rise to electric response of 

 galvanometric negativity, the response being mono-phasic. Application of 

 thermal and chemical stimulus produced similar results (fig. 9). 



Experiment 5. — The second electrode was in this case thrust into the 

 nerve of the plant about 1 cm. behind the first electrode. The response is 



