262 PLANT RESPONSE 



one above the other on the same revolving drum. On 

 applying a stimulus, say thermal, at A, it will be found, 

 after the lapse of a definite interval, that both spots of light 

 are deflected simultaneously, proving the concomitance of the 

 mechanical and electrical effects. Such a record has been 

 given already, in fig. 26. If we make a mark on the 

 revolving drum at the moment of the application of stimulus, 

 and a second mark when the electrical (and, in this particular 

 case, also the mechanical) response is initiated, we can, with 

 the previous knowledge of the speed of the drum, determine 

 the time taken by the excitation to travel from A to B, and 

 thus find the velocity of transmission for that specimen by 

 electrical means. 



A further refinement of this method lies in the use of two 

 galvanometers instead of one, the slight lag of response, 

 caused by galvanometric inertia, being in this way eliminated. 

 Particulars regarding this will be found elsewhere. 



It will be seen, then, that in the electromotive method 

 we have a second means by which to determine the velocity 

 of transmission of excitation in what are known as ordinary 

 plants. I shall now describe experiments performed by this 

 method. The peduncle of Biopliytum is leafless. That it 

 does transmit stimulus is seen nevertheless when we excite 

 it at any point. Excitation will then be found transmitted 

 through it to the main stem, from which it travels outwards 

 to different leaves, a fact evidenced by the serial fall of 

 leaflets in a centrifugal order. In such a peduncle I have 

 determined the velocity of transmission by the electromotive 

 method. The distance between the points A and B was 

 4'6 cm, ; the time taken for transmission was 127 seconds. 

 The velocity is thus found to be 37 mm. per second. 



Similarly, in the stem of Ficus religiosa, I found velocity of 

 transmission to be 9/4 mm. per second, which is almost the same 

 as that in the stem of the so-called 'sensitive' plant Mimosa. 



From the experiments carried out on the electrotactile 

 method it will be seen that excitation is conducted along 

 a plant-tissue from cell to cell, as a contractile wave. We 



