778 
Bose . — On Diurnal Variation of 
that obtained in spring. The excitability is here not totally abolished in 
the morning, but reaches a minimum about 8 a.m. ; the sensitiveness is then 
gradually enhanced in a staircase manner. 
Table II. 
Showing the relation between hour of the day, temperature, and excitability. (Summer specimen.) 
Hours of 
day . 
Temperature . 
Amplitude of 
Response. 
Hours of 
day. 
Temperature. 
Amplitude of 
Response. 
i p.m. 
OJ 
GO 
O 
P 
22 mm. 
1 a.m. 
26° C. 
2 i*c; mm. 
2 „ 
38° „ 
23 
2 „ 
26° „ 
20 „ 
3 „ 
38° „ 
2 4‘5 >, 
3 „ 
2 5‘5° 5J 
i8‘5 „ 
4 „ 
37° >, 
28 „ 
4 » 
25-5%, 
17 
5 » 
35*5° ,, 
29 „ 
5 » 
25-5° „ 
16 
6 „ 
33° „ 
27 » 
6 „ 
26° „ 
15 
7 >, 
3i° „ 
26 ,, 
7 „ 
27° „ 
14 » 
8 „ 
30° » 
26 „ 
8 „ 
2 9° „ 
13 
9 » 
2 9° » 
25 
9 » 
30-5° » 
11 
IO ,, 
2 7° „ 
24*5 » 
10 „ 
33° » 
16 „ 
ii „ 
27° „ 
24 „ 
11 » 
35° 
17 
12 „ 
26*5° „ 
22-5 „ 
12 „ 
37° u 
21 
Summary. 
An account is given of the experimental method by which the moto- 
excitability of Mimosa is gauged, every hour of the day and night, by the 
amplitude of the response to a testing stimulus. This is effected by means 
of automatic devices which excite the plant periodically by an absolutely 
constant stimulus, and record the corresponding mechanical response. 
From the record thus obtained, it was found that the excitability of the 
plant is not the same throughout the day, but undergoes a variation 
characteristically different at different times of the day. In a typical case 
in spring, the excitability attained its maximum value at i p.m. There was 
then a continuous fall in the excitability, the minimum being reached at nine 
the following morning. The plant at this time was practically insensitive. 
The moto-excitability was then gradually enhanced in a staircase manner 
till it again reached a maximum at i p.m. 
Investigations are also described for the determination of the influence 
of periodically changing external conditions on the diurnal variation of 
excitability. 
The effect of sudden darkness was found to induce a transient depres- 
sion, followed by revival of excitability. The effect of persistent darkness 
was to induce a depression. 
Exposure to light caused a transient depression, followed by an 
enhancement of excitability. 
Excessive turgor induced a diminished response. 
Lowering of temperature induced a depression of excitability, culmi- 
nating in an abolition of response. The after-effect of excessive cold was 
a persistent depression of excitability. 
