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 i 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. loi 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 



