certain Tropical Trees . 81 
leaflets and thready and thus not to impede any movement. 
A knot was made on one side of the thread, which was then 
gently tightened and an India-ink mark made where the 
thread passed through the opposite leaflet. By these means 
the distance between each pair of opposite leaflets, at the 
commencement of the experiment, was known. Any upward 
movement, whereby the leaflets approach a more horizontal 
position, was indicated by a greater length of thread becoming 
included between the leaflets, a downward movement by 
a bagging of the thread. The positions occupied by the 
leaflets, at different times of day and night, could then be 
compared. 
Fourteen pinnate leaves, each two feet or more in length, 
and each bearing from three to seven threaded pairs of leaflets, 
were observed. The threads were passed through and marked 
between 7.30 and 9 o’clock on Monday. 
The leaves chosen were mostly young, still more or less 
pendent, and brilliantly green ; some, however — and reference 
will later be made to these— had reached their mature fixed 
positions ; and in these the petioles of the leaflets seemed to be 
quite rigid, although, as will be seen, they were still capable of 
some movement. 
Allowing ( + ) to stand for those leaflets which had become 
more horizontal (since in so doing they included more thread 
than between knot and India-ink mark) ; ( = ) to denote those 
whose positions were unchanged; (— ) those which came to 
hang more vertically, the following numbers represent the 
results obtained : 
( + ) (=) (-) 
Monday, 1.40 p.m. 31 32 15 = 78 total leaflets observed. 
4.30 „ (sunny) 28 25 21=74 » » 
8.30 ,, all the leaves hanging down, most so that the laminae of 
opposite leaflets were parallel. 
(+) for (-) 
43 23 7=73 
Tuesday, 7.30 a.m. 
