THE ELECTRO-MOTIVE RESPONSE OF PLANTS 19 



responses of mechanical depression and galvanometric nega- 

 tivity by up-curves. The erectile movement and galvano- 

 metric positivity will, conversely, be represented as down. 



A few words may be said here as regards the syn- 

 chronism between the two forms of response. The excitatory 

 molecular change takes place instantaneously, and the 

 electro-motive variation is, as far as can be judged, strictly 

 concomitant with it. This is shown by the rheotomic 

 method of observation, described in Chapter IV. It will there 

 be seen that a very considerable electro-motive change has 

 already been induced, in a period so short as X)i of a second 

 after the reception by the tissue of the stimulating shock. 





FIG. 13. Simultaneous Mechanical (M) and Electrical (E) Responses in Biophylum 

 These responses are seen to take place at the same moment. 



In the electrical response, then, of highly excitable tissues 

 there is practically no latent period. But if the same elec- 

 trical variation be recorded by the galvanometer, there will 

 be a lag in the response, owing to the inertia of the galva- 

 nometer needle. Similarly, in the mechanical response, 

 though the excitatory reaction is immediate, yet the motile 

 response is delayed, by the antagonistic actions of the upper 

 and lower halves of the pulvinus, the sluggishness of the 

 tissue, and the mechanical inertia of the indicating leaf. 

 The latent period of the mechanical response of a vigorous 

 Mimosa, owing to all these causes, I find to be about 

 twenty-four-hundredths of a second. But this may be still 

 further prolonged when the tissue is in a state of depressed 



