358 Dr. Bruce’s Account of a 
regular and gradual. Afterwards, when the leaves return to 
their former fituation, which is commonly in a quarter of an 
hour or lefs, it is in fo flow a manner as to be almoft imper- 
ceptible. 
On flicking a pin into the univerfal petiolus at its origin, 
the leaf next it, which is always on the outer fide, moves firft ; 
then the firft leaf on the oppoiite fide, next the fecond leaf on 
the outer, and fo on. But this regular progreflion feldom con- 
tinues throughout ; for the leaves on the outer fide of the pinna 
feem to be affe&ed both more quickly, and with more energy, 
than thofe of the inner, fo that the fourth leaf on the outer 
fide frequently moves as foon as the third on the inner ; and 
fometimes a leaf, efpecially on the inner fide, does not move 
at all, whilft thofe above and below it are affedled in their pro- 
per time. Sometimes the leaves at the extremity of the petio- 
lus move fooner than feveral others which were nearer the 
place where the pin was put in. 
On making a compreflion with a pair of pincers on the uni- 
verfal petiolus, between any two pair of leaves, thofe above 
the comprefled part, or nearer the extremity of the petiolus, 
move fooner than thofe under it, or nearer the origin ; and fre- 
quently the motion will extend upwards to the extreme leaf, 
whilft below it perhaps does not go farther than the neareft 
pair. 
If the leaves happen to be blown by the wind againft one 
another, or againft the branches, they are frequently put in 
motion ; but when a branch is moved gently, either by the 
hand or the wind, without ftriking againft any thing, no 
motion of the leaves takes place. 
When left to themfelves in the day-time, fhaded from the 
fun, wind, rain, or any difturbing caufe, the appearance of 
n the 
