768 
Bose.- — On Diurnal Variation of 
allowing its main pulvinus to absorb water. The result is seen in the next 
record (Fig. 7), where water was applied on the pulvinus after the second 
response. It is seen how a depression of moto-excitability results from 
excessive turgor brought on by absorption of water. In such cases, how- 
ever, the plant may accommodate itself to the abnormal condition and 
gradually regain its normal excitability in the course of several hours. 
(3) Influence of Temperature. 
The moto-excitability of the pulvinus of Mimosa is greatly modified 
under the influence of temperature. For the purpose of this investigation 
I enclosed the plant in a glass chamber, raising the temperature to the 
desired degree by means of electric heating. Responses to identical stimuli 
Fig. 8. Effect of moderate cooling during a period shown by horizontal line below. 
Moderate depression followed by quick restoration. 
were then taken at different temperatures. It was found that the effect of 
heightened temperature, up to an optimum, was to enhance the amplitude 
of response. Thus with a given specimen it was found that while at 22 0 C. 
the amplitude of response was 2.5 mm., it became 22 mm. at 27 0 C., and 
52 mm. at 32 0 C. The excitability is enhanced under rising, and depressed 
under falling temperature. The moto-excitability of Mimosa is practically 
abolished at a temperature of about 19 0 C. * 
Effect of lowering of temperature. A simple way of exhibiting the 
effect of lowering of temperature is by artificial cooling of the pulvinus. 
This cannot very well be done by application of a stream of cooled water, 
because, as we have seen, absorption of water by the pulvinus is attended by 
a loss of excitability : glycerine has, however, no such drawback. This fluid 
