Dr. Bruce’s- Account of See. 
them move alternately, or, in fhort, in any order you'pleafe, by 
touching in a proper manner the leaf you wifh to put in mo- 
tion. But if the impreffion, although made on a tingle leaf, 
he Itrong, all the leaves on that pinna, and fometimes on the 
neighbouring ones* will: be affected by it. 
. What at firft feemed furprifmg was-,, that notwithflanding 
this apparent fenlibility of the leaf,- I could with a pair of 
fharp feiffars make large incilions in it,, without occafioning the 
fmalleft motion ; nay, even cut it almofl entirely off, and the 
remaining part dill continue unmoved ;; and’ that then, by 
! touching the wounded leaf with the finger or point of the 
feiffars, motion would take place as if no injury had been./ 
: offered. But, on further examination, I found, that although 
: the leaf was the offenfible part which moved, it was in 'fact 
entirely paflive, and that the petiolus was the feat both of fenfe 
and adtion : for although the leaf might be cut in pieces, or 
fqueezed with great force,, provided its direction was not 
changed, without any motion being oecafioned; yet \ if the im- 
preffion on the leaf was made in fuch a way as to affedt the 
petiolus, the motion took place. When, therefore,. I wanted" 
to confine the motion to a fingle leaf, I either touched it fo as 
only to affedf its own petiolus, or, without meddling with the 
leaf, touched the petiolus with any fmall-pointed body, as a pin > 
or knife. 
By compreffing the univerfal petiolus near the place where 
a partial one comes out, the leaf moves in a few ieconds, in the 
fame manner as if you had touched- the partial petiolus. 
Whether the impreffion be made bvpundfure, percuffion, or 
:compreffion, the motion does not inffantly follow; generally 
Several feconds intervene, and then it is not by a jirk, but 
regular 
