120 RESEARCHES ON IRRITABILITY OF PLANTS 



•17 second. The identity of these values shows that the 

 inertia of the recorder has but Httle effect on the results 

 obtained. 



The latent period in any given specimen of the pulvinus 

 of Mimosa is, as we have seen, under uniform conditions 

 extremely constant. It differs, however, in different speci- 

 mens and from season to season. A thin specimen has in 

 general a shorter latent period than one which is stouter. 

 Perhaps this fact is illustrated, with a certain exaggeration, 

 in the case of Neptunia, the leaf and pulvinus of which are 

 comparatively thick. In any case, we have already seen 



Fig. 73.— Record of latent period of Neptunia with 10 D.V. recorder. 



that in its responsive movements, relatively to Mimosa 

 pudica, it is very sluggish. In order to determine the latent 

 period I employed a slow vibrator, that is to say, one which 

 vibrates with a frequency of 10 per second. It will be seen 

 by reference to fig. 73 that the responsive movement began 

 after the sixth dot, the latent period being thus '6 second, 

 or six times the value of the average latent period in 

 Mimosa. 



With Mimosa pudica I have carried out more than a 

 hundred different determinations, and give below a tabular 

 statement of seventy of those values which occurred 

 most frequently amongst these. Specimens giving a latent 



