770 
Bose. — On Diurnal Variation of 
I may now briefly recapitulate some of the important results : darkness 
depresses, and light exalts the moto-excitability. Excessive turgor de- 
presses motility. Still more marked is the effect of temperature. Lowering 
of temperature depresses and finally abolishes the moto-excitability : rise of 
temperature enhances it up to an optimum temperature, but beyond this 
point the excitability undergoes depression. The change in excitability 
Fig. io. Effect of temperature above optimum. Note depression of excitability induced by high 
temperature, and gradual restoration on return to normal. 
induced by the variation of external condition is not immediate ; the induced 
effect, generally speaking, lags behind the inducing cause. 
III. Diurnal Variation of Excitability. 
I will now give automatic records of responses taken once every hour 
for twenty-four hours. They prove conclusively the diurnal variation of 
excitability in Mimosa . After studying in detail the variations characteristic 
of particular times of the day, I will endeavour to correlate them with the 
effects brought on by the periodic changes of the environment. 
As a typical example I will first give a record obtained in the month 
of February, that is, say in spring. From this it will not be difficult to 
follow the variations which take place earlier in winter or later in summer. 
The record given in Fig. n was commenced at 5 p.m., and con- 
tinued to the same hour next day. The first thing noticeable is the 
periodic displacement of the base-line. This is due to the nyctitropic 
movements of the leaf. It should be remembered that the up movement 
of the leaf is represented by down-curve, and vice versa. After the maximum 
fall of the leaf, which in this case was attained at 9 p.m., there followed 
