IDl-t] on Plant-Autographs and their Revelations 189 



hydro -mechanical theory must necessarily fall to the ground, if excita- 

 tion can be effected without any mechanical disturbance whatsoever. 

 I have shown that excitatory impulse is initiated under the polar 

 action of current in the complete absence of any mechanical disturb- 

 ance, the intensity of the current being so feeble as not to be 

 perceived even by the very sensitive human tongue. 



(2) If it can be shown that physiological changes induce appro- 

 priate variation in the velocity of transmission of the impulse. 



(8) If the impulse in the plant can be arrested by dififerent 

 physiological blocks by which nervous impulse in the animal is 

 arrested. 



For the last two investigations the research resolves itself into 

 the accurate measurement of the speed with which an impulse in the 

 plant is transmitted, and the variation of that speed under changed 

 condition. A portion of the tissue at C may, for example, be sub- 

 jected to the action of cold, or of a poison (Fig. 12). In order 

 to find the speed of normal transmission, we apply an instan- 

 taneous stimulus, say, of an electric shock, at B, near the pulvinus 

 A short interval, the latent period, will elapse between the application 

 of stimulus and the beginning of responsive movement. After the 

 determination of the latent period, we apply stimulus once more at 

 A, and observe the time which elapses between the application of 

 stimulus and the response. The difference between the two periods 

 gives us the time required for the excitation to travel from the point 

 of application of stimulus at A, to the responding organ at B ; hence 

 we obtain the speed of impulse in the plant. The experiment is 

 repeated once more, after the application of a given agent at C. If 

 the speed undergoes any variation, it must be due to the action of 

 the given agent. 



Determination of Speed of Excitatory Impulse m 

 Plants.* 



As relatively long intervals have to be measured in the deter- 

 mination of velocity, the recorder has its frequency adjusted to ten 

 vibrations per second ; hence the space between successive dots 

 represents an interval of one-tenth of a second. In Fig. 13 is given 

 a record for determining the velocity of transmission. The two 

 lower figures give practically identical results of successive experi- 

 ments when stimulus was applied at a distance of 30 mm. The 

 uppermost is the record for du'ect stimulation. From these it is 

 seen that the interval between stimulus and response is 1*6 second, 



* For a more detailed account confer : 



BosE — An automatic method for the investigation of velocity of trans- 

 mission of excitation in Mimosa. Phil. Trans, of Royal Society, Series B, 

 Vol. CCIV. 



BosE — Researches on Irritability of Plants (Longmans, Green, 1913). 



