760 
Bose . — On Diurnal Variation of 
for the enhancement of the moto-excitability ; it was, nevertheless, found 
that though the excitatory response was only moderate at that period of 
night when the temperature was at its minimum, yet the excitability was 
altogether abolished at another period when the temperature was several 
degrees higher. The obscurities which surrounded the subject were only 
removed as a result of protracted investigation and comparison of continuous 
automatic records made by the plant itself during several months, beginning 
with winter and ending in summer. 
The question whether a plant like Mimosa exhibits diurnal variation of 
excitability can be experimentally investigated by subjecting the plant at 
every hour of the day and night to a test-stimulus of uniform intensity, and 
Fig. i. Diagrammatic representation of the complete apparatus for determination of diurnal 
variation of excitability. Petiole of Mimosa , attached by thread to one arm of lever L ; writing 
index w traces on smoked glass plate G the responsive fall and recovery of leaf, p, primary, 
and s, secondary, of induction coil. Exciting induction passes through the plant by electrodes e, e'. 
a, accumulator, c, clockwork for regulating duration of tetanizing shock. Primary circuit of coil 
completed by plunging rod r dipping into cup of mercury m. 
obtaining the corresponding mechanical responses. Under these circum- 
stances the amplitude of response at anytime will serve as a measure of the 
excitability of the plant at the particular time. Any periodic fluctuation of 
response will then demonstrate the periodic character of variation of ex- 
citability. 
The investigation thus resolves itself into — 
1. The successful construction of a Response Recorder which will 
automatically record the response of the plant to uniform periodic stimula- 
lation at all hours of day or night ; 
2. The study of the effects of various external conditions on ex- 
citability ; 
