Moto-exci lability in Mimosa . 775 
that particular case whose diurnal variation of excitability is given in 
Fig. 11. 
Table I. 
Showing the relation between hour of the day, temperature, and excitability. (Spring specimen.) 
Hours of 
day. 
Temperature. 
Amplitude of 
response. 
Hours of 
day. 
Temperature. 
Amplitude of 
response. 
5 
p.m. 
28° C. 
28 
mm. 
5 
a.m. 
20° C. 
5 
mm. 
6 
n 
2 5 * 5 ° „ 
28 
n 
6 
11 
20-5° ,, 
4*2 
11 
7 
11 
24*5 „ 
27 
19 
7 
11 
21° „ 
3*5 
1 1 
8 
91 
23° „ 
23*5 
? 1 
8 
11 
22 ° „ 
2-5 
1 9 
9 
22° „ 
21-5 
11 
9 
11 
24 ° „ 
0 
1 1 
10 
11 
21° „ 
18 
11 
10 
1 1 
26° „ 
6 
11 
11 
20-5° „ 
T 5 
11 
11 
11 
26*5° „ 
i 5’5 
11 
12 
20° ,, 
13 
11 
12 
1 1 
28° „ 
22*5 
11 
1 
a.m. 
20° „ 
10 
19 
1 
p.m. 
28° „ 
26 
2 
11 
20° „ 
8 
11 
2 
11 
28-5° ,, 
28 
11 
3 
11 
20° „ 
7'5 
11 
3 
11 
28-5° „ 
28 
u 
4 
19 
19 * 5 ° » 
6 
11 
4 
1 1 
29° » 
28 
11 
From the data given in the table, two curves have been obtained. One 
of these shows the relation between the hours of the day and temperature ; 
the other exhibits the relation between the hours of the day and the excita- 
bility as gauged by the amplitude of response (Fig. 16). It will be seen 
that there is, broadly speaking, a marked resemblance between the two 
curves, which, however, are not coincident. The minimum temperature, 
for example, was attained at about 4 a.m., but the excitability was not 
reduced to a minimum till several hours later. This want of coincidence is 
probably due to the following causes : 
1. The influence of temperature on excitability is, as has been shown, 
not immediate. Hence there is a lag between the cause and the effect 
induced. 
2. There are, again, other factors, such as variations of light and 
turgor, which affect the excitability. But the period of maximum effect 
induced by any of these does not necessarily coincide with that induced by 
temperature. 
We may now discuss in greater detail the diurnal variation of excita- 
bility in Mimosa , taking the typical case, the record of which is given in 
Fig. 11. The temperature here is seen to remain almost constant, and at 
an optimum, from 1 to 5 p.m., the condition of light is also favourable. 
Hence the excitability is found to be constant, and at its maximum, between 
these hours. The temperature begins to fall in the evening after 6 p.m., 
and there is, in addition, the depressing action of gathering darkness. 
Owing to the time-lag, the fall of excitability does not commence imme- 
diately at 6 p.m., but an hour afterwards, and continues till the next morning. 
Various factors, moreover, conspire about this time to bring about a maxi- 
mum depression of excitability. First, we have the cumulative effect of 
twelve hours’ darkness ; secondly, there is a diminution of moto-excitability 
3 G 2 
