358 Dr. Bruce's Account of a 



regular and gradual. Afterwards, when the leaves return to 

 their former lituation, which is commonly in a quarter of an 

 hour or lefs, it is in fo flow a manner as to be almofl imper- 

 ceptible. 



On flicking a pin into the univerfal petiolus at its origin, 

 the leaf next it, which is always on the outer iide, moves firft ; 

 then the firfl: leaf on the oppofite fide, next the fecond leaf on 

 the outer, and fo on. But this regular progreffion feldom con- 

 tinues throughout ; for the leaves on the outer fide of the pinna - 

 leem to be affected 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 mner fide, does not move 

 at all, whilft thofe above and below it are afFe£ted 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 compreflcd 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 iii'- 

 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, (haded from the 

 fun, wind, rain, or any difturbing caufe, the appearance of 



7 ' the 



