77i 
Moto-excitability in Mimosa. 
a reverse movement : the highest erection, indicative of maximum turgor, 
was reached at 6 a.m. The leaf then fell slowly and reached a middle 
position at noon. The extent of the nyctitropic movement varies in 
individual cases ; in some it is slight, in others very large. The erectile 
movement began, as stated before, at about 9 p.m. ; in some cases, however, 
it may occur as early as 6 p.m. 
In following the characteristic variations of response, occurring through- 
out the day, we find that while they are practically uniform between the 
hours of 5 and 7 p.m., a continuous decline is manifested after setting in of 
darkness (6 p.m.) ; the fall of excitability continues even after sunrise 
Fig. 11. Record for twenty-four hours, exhibiting diurnal variation of excitability (spring 
specimen'). The displacements of base-line are due to nyctitropic movements. 
(6.30 a.m.), response being practically abolished at 9 a.m. The excitability 
is then gradually restored in a staircase manner, the maximum being reached 
after 12 noon. After attaining this, the excitability remains constant till 
the evening. It will be noticed that the amplitude of response at 5 p.m. on 
the second day was the same as the corresponding response on the 
previous day. 
The results of this and numerous other records taken in spring may be 
summarized as : 
1. The maximum excitability of Mimosa is attained at about 1 p.m., 
and remains constant till the evening. 
2. The excitability, generally speaking, undergoes a continuous decline 
from evening to morning, the response being practically abolished at or 
about 9 a.m. 
