VOL. LXXV.] PHILOSOPHICAL TRANSACTIONS. 1 1 



sensibility of the leaf, I could with a pair of sharp scissars make large incisions 

 in it, without occasioning the smallest motion ; nay, even cut it almost entirely 

 off, and the remaining part still continue unmoved ; and that then, by touching 

 the wounded leaf with the finger or point of the scissars, motion would take 

 place as if no injury had been offered. But, on further examination I found, 

 that though the leaf was the ostensible part which moved, it was in fact entirely 

 passive, and that the petiolus was the seat both of sense and action : for though 

 the leaf might be cut in pieces, or squeezed with great force, provided its direc- 

 tion was not changed, without any motion being occasioned ; yet if the impres- 

 sion on the leaf was made in such a way as to affect the petiolus, the motion took 

 place. When therefore I wanted to confine the motion to a single leaf, I either 

 touched it so as only to affect its own petiolus, or, without meddling with the 

 leaf, touched the petiolus with any small-pointed body, as a pin or knife. By 

 compressing the universal petiolus near the place where a partial one comes out, 

 the leaf moves in a few seconds, in the same manner as if you had touched the 

 partial petiolus. 



Whether the impression be made by puncture, percussion, or compression, 

 the motion does not instantly follow ; generally several seconds intervene, and 

 then it is not by a jerk, but regular and gradual. Afterwards, when the leaves 

 return to their former situation, which is commonly in a quarter of an hour or 

 less, it is in so slow a manner as to be almost imperceptible. On sticking a pin 

 into the universal petiolus at its origin, the leaf next it, which is always on the 

 outer side, moves first ; then the first leaf on the opposite side, next the 2d leaf 

 on the outer, and so on. But this regular progression seldom continues through- 

 out ; for the leaves on the outer side of the pinna seem to be affected both more 

 quickly, and with more energy, than those of the inner, so that the 4th leaf on 

 the outer side frequently moves as soon as the 3d on the inner ; and sometimes 

 a leaf, especially on the inner side, does not move at all, while those above and 

 below it are affected in their proper time. Sometimes the leaves at the extre- 

 mity of the petiolus move sooner than several others which were nearer the place 

 where the pin was put in. On making a compression with a pair of pincers on 

 the universal petiolus, between any two pair of leaves, those above the com- 

 pressed part, or nearer the extremity of the petiolus, move sooner than those 

 under it, or nearer the origin ; and frequently the motion will extend upwards 

 to the extreme leaf, while below it perhaps does not go farther than the nearest 

 pair. 



If the leaves happen to be blown by the wind against each other, or against 

 tlie branches, they are frequently put in motion ; but when a branch is moved 

 gently, either by the hand or the wind, without striking against any thing, no 

 motion of the leaves takes place. When left to themselves in the day-time, 



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