772 
Bose.— On Diurnal Variation of 
3. From 8 a.m. to 12 noon, the excitability is gradually enhanced in 
a staircase manner, till the maximum excitability is reached near 1 p.m. 
I have obtained numerous records in support of these conclusions, some 
of which are reproduced in the following figures. In these cases responses to 
uniform stimuli at intervals of half an hour were taken at different parts of 
the day, the recorder employed being of the Resonant type. 
Mid-day record. The record of daily periodicity previously given 
shows that the excitability reaches its maximum after 12 noon, and that it 
remains constant at the maximum value for several hours. This fact is 
Fig. 12. Mid-day record from noon to 3 p.m. exhibiting uniform excitability. Responses taken 
once every half-hour. 
fully borne out in the following record obtained with a different specimen 
(Fig. 12). The responses were taken here from noon to 3 p.m., once every 
half-hour. 
Evening record. The record given in Fig. 11 shows that the amplitude 
of response falls continuously after 6 p.m. It might be thought that the 
diminished amplitude in the first part may be due to the natural nyctitropic 
fall of the leaf. The range of the pulvinar movement being limited, it is 
clear that the extent of the responsive fall must become smaller on account 
of the natural fall of the leaf during the first part of the night. That this is 
not the whole explanation of the decline of response in the evening will be 
clear from certain facts which I will presently adduce. It was stated that 
the leaf of Mimosa exhibits nyctitropic fall from 6 to 9 p.m., after which 
there is a reverse movement of erection. In certain specimens, however, 
the erectile movement commenced as early as 6 p.m. It is obvious that in 
these latter cases diminution of amplitude of response cannot be due to the 
reduction of the range of movement of the leaf. In Fig. 13 is given a series 
of records from 6 to 10 p.m. obtained with a leaf in which erectile move- 
ment had commenced early in the evening. Though the fullest range of 
