192 RESEARCHES ON IRRITABILITY OF PLANTS 



after the positive, the interval being equal to the latent 

 period of the responding pulvinus. 



I have shown that the average latent period of the 

 primary pulvinus of Mimosa is *i second. In unfavourable 

 circumstances even, I have never found it to exceed 

 •3 second. The latent period of the leaflet of Biophytum 

 or Averrhoa is about *4 second. The latent period of the 

 responding organs of the various sensitive plants mentioned 

 may therefore be taken as less than 1 second. If between 

 the positive and negative response there is any relation 

 of cause and effect, then the negative should occur within 

 a second of the positive. But this is by no means the case. 

 Referring to fig. 101 we find that the positive impulse 

 reached the pulvinus 4 seconds after the application of 

 the stimulus, and instead of the excitatory response taking 

 place within a second, we find that it did not occur till 

 37 seconds after ! I give below a table which shows the 

 very lengthened periods which are often found to elapse 

 between the arrival of the positive impulse and the initiation 

 of the excitatory response : — 



Table V. — Showing Difference of Time between the Arrival of 

 Positive Impulse and the Initiation of Excitatory Response 



The results just described, together with the fact that 

 we may have a positive response without the subsequent 

 negative (cf. lower record fig. 103), show conclusively that 



