TRANSMISSION OF EXCITATORY WAVES IN PLANTS 24 1 



From a separate experiment, by direct stimulation of the 

 base of the petiolule, it was found that the latent period of 

 the leaflet was so small a fraction of a second, as, for our 

 present purpose, to be negligible. In this way, in my first 

 experiment, I found the time taken by the excitation to travel 

 the distance of 27 mm. between B and L to be 14-3 seconds. 

 I allowed the plant a period of rest of three minutes, and 

 again performed the experiment under similar conditions. 

 The time taken was found to be I4"5 seconds, which is 

 practically the same, within experimental error, as the result 

 first obtained. The slight difference was due to the residual 

 effect of fatigue. In any case, the extreme difference between 

 the two results amounts to less than 1-4 per cent. — or 7 per 

 cent, from the mean value of i4'4. From this we find that in 

 the particular plant under experiment the velocity of trans- 

 mission in a centripetal direction was i-88 mm. per second. 

 In order to show how consistent successive results are, I give 

 successive time-intervals taken by stimulus in two different 

 cases, to travel the intervening distances. 



Case I. Time-interval in first experiment I2'6 seconds. 



„ second „ 12-9 ,, 



Case 2. „ first ,, 14-8 „ 



„ second „ 15 ,, 



In all these cases, the second experiment was undertaken 

 after an interval of rest of three minutes. The slight re- 

 tardation uniformly observed is due, as already explained, to 

 residual fatigue. It is, however, so small as to be negligible. 

 At any rate, making allowance for all possible sources of 

 uncertainty, the variation of these determinations will be less 

 than 2 per cent. 



We have to remember that, owing to the slow velocity of 

 transmission of impulses in plants, and also to the com- 

 paratively great length of tissue, that can, when necessary, 

 be brought under examination, the total interval of time that 

 has to be observed may be made as large as twenty to forty 

 seconds. In such periods, a mean error of even "2 second 



K 



