Moto-excitability in Mimosa. 77 9 
Excitability was enhanced by rising temperature up to an optimum ; 
above this point a depression was induced. 
The induced variation of excitability lags behind the inducing cause. 
There is a relation between the recurrent changes of external conditions 
and the diurnal variation of excitability. The periodic variation of light, 
temperature, and turgor, as well as the phenomenon of lag, are factors 
which determine the periodic variation of excitability observed in the 
plant. 
Postscript. It should be explained that the term ‘ moto-excitability * is 
intended to convey the idea that the observed periodic variation is probably 
to be attributed in part to variation in the motility of the pulvinus, as well 
as to variation in the excitability of the leaf. That the latter is the 
predominant factor appears from the fact that the minimal intensity of 
stimulus required in the afternoon was found to be only about one-fifth of 
that in the forenoon. 
It is of interest to compare the results here recorded with those of 
Millardet (‘Nouvelles Recherches sur la Periodicite de la Tension chez la 
Sensitive,’ Strasbourg, 1869). 
