SEN 



r^n at other times, and by accidents, there requiring no more 

 •han the touching of the plant to make it clofe its leaves at any 

 time of the day, which it foon afterwards naturally opens 

 ao-ain. This is pecuHar to this plant, and refembles the 

 lAion of an animal which had been injured or frighted. A 

 clofe obfervation alfo of the manner in which this is per- 

 formed, will give many hints towards the finding of its caufe. 



It is a very difficult thing to touch the leaf of a vigorous 

 fenfitive plant fo lightly, as not to make it clofe ; its fenfation 

 is extremely delicate, and its large rib or nerve, which runs 

 along its middle, is as it were a hinge, on which the two 

 halves of the leaf move when they turn upon being touched, 

 till they (land ereft, and by that means meet one another. 



The flightell touch imaginable gives this motion to the 

 fide of the leaf which is touched, which is communicated 

 immediately to the other fide, or half, and they move to- 

 gether ; and if the touch has been a very little rougher, the 

 oppofite leaf on the fame rib receives the imprefiion, and 

 clofes up in the fame manner with that which was actually 

 touched. 



Nor is this all, for when the two fides of each of thefe 

 leaves move upwards, the pedicle of each half moves up- 

 wards at the fame time, and by this means they, in fome 

 meafure, approach towards each other, and make the angles 

 of their pedicles with the mam rib, or italk of the compofite 

 ieaf, lefs than before ; and the total motion of each leaf is 

 compofed of .hefe two nKnions. 



If tlie touf-h be ilill rougher, the whole arrangement of 

 leaves on the fame rib feeis its influence on each fide, and all 

 dole in the fame manner with the fingle pair in the preceding 

 IP fiance ; and if the touch be yet ftronger than this, the r:b 

 itfelf feels it, and attempts to clofe in its way ; moving itfelf 

 upwards towards the branch from which it is produced, juft 

 as the fingle pedicles of the leaves did towards it : and if the 

 touch be yet more hard and rough, the very branches have 

 the fenfation propagated to tliem, and apply themfelves to 

 the main ftera, or trunk of the (hrub, as the fimple leaves did 

 before to their rib, and that rib to the branch ; fo that the 

 whole plant in this ftate forms itf.-lf from a very complexly 

 branched figure, into a fort of ftraight cylindric one. That 

 motion which has, of all others, the greatelt effett upon this 

 plant, is a (baking one. 



Thefe three motions of the plant are performed by means 

 of three diitinft and fenCble articulations ; the firft that of 

 the fingle leaf to its pedicle, the fecond that of the pedicle to 

 its branch, the third that of the bi-anch to the trunk. The 

 primary motion of all which, is the clofing of tlie two halves 

 of the leaf upon their rib, which ought alfo to be per- 

 formed in a fimilar manner, and by a fimiiar articulation ; 

 this, however, is much lefs vifible than the others. 



Thefe motions are wholly independent of one another, as 

 may be proved by experiment. It Ihould appear, that if 

 the ftalks are moved, and coUapfe towards the branches, or 

 thefe towards the trunk, that the leaves, whole motion is 

 •ufiially primary to thefe, (hould be alfeded alfo ; ye; expe- 

 riment proves, that it is poffiblc to touch the branches in 

 fuch a manner, as to affoft them only, and make th'm .ipp'y 

 themfelvi's to the trunk, while the leaves feel nothip<; of the 

 touch ; but this cannot be, unlefs the branches are (o dif- 

 pofcd, as that they can fall to the trunk without fuffering 

 their leaves to touch any other part of the plant in their pa(- 

 fagc-, becaufe, if they do, they immcdiatily become afleftcd. 



Winds and heavy rains caufe the fenfitive plants to (hut 

 up their leaves, while eafy (bowers do not at all affect them ; 

 it IS plain hence, that the agitation of the plant by the wind, 

 and the ftrokcs given by the large and halty drops of rain, 

 are what caufe the contradtion. 



SEN 



By whatever accident the plant has been made to clofe its 

 leaves, it always regularly opens them again afterwards. 

 This, however, requires diiferent times, according to feveral 

 tircumitances, as the time of the day, the feafon of the year, 

 and the more and lefs vigorous and healthy (late of the plant ; 

 fometimes this is done in ten minutes, fometimes it requires 

 half an hour ; and the manner is not lefs different than the 

 time, for fometimes the leaves unfold themfelves firft, and 

 fometimes the branches, whereas fometimes all is done at 

 once, and the whole plant feems in motion at a time. 



In endeavouring to account for the motions of this plant, 

 the gentlemen above named have conjeftured that they are 

 performed by means of a fort of very nice and fine hinges, 

 which communicate one with another by means of very 

 minute and (lender cords, which occafion them to aft as we 

 fee when the plant is fufiiciently difturbed, and thefe cords 

 fliaken ; and what gives a (trong probability to this con- 

 jefture is, that the decayed and dying leaves of the plant 

 perform this motion as regularly and vigoroufly, as thofe 

 which are frefh and full of juice. 



It feems plain, that while the juices are evaporating, and 

 the parenchymatous fubitance of the leaves drying up, thefe 

 more folid parts, the lines and cordages, retain their figure ; 

 and, confequently, if it is by means of thefe that the motion 

 is always performed, it will be as well performed in thefe as 

 in the frelher leaves, which could not be the cafe were it 

 owing to the juices. 



The natural opening and fliutting of the leaves of this plant 

 at night and morning, are not fo fixed but that they are 

 variable alfo, according to circumitances of place, tempe- 

 rature, &c. 



In the month of Auguft, a fenfitive plant was carried in 

 a pot out of its ufual place into a dark cave, the motion that 

 it received in the carriage fliut up its leaves, and they did not 

 open till twenty-four hours afterwards ; at this time they be- 

 came moderately open, but were afterwards fubjeft to no 

 changes at night or morning, but remained three days and 

 nights with their leaves in the fame moderately open itate. 

 At the end of this time they were brought out again in the 

 air, and then recovered their natural periodical motions, (hut- 

 ting every night and opening every morning, as naturally 

 and as ilrongly, as if it had not been in this forced ftate ; and 

 while in the cave, it was obferved to be very little lefs af- 

 fefted with the touch than when abroad in the open air. 



Repeated experiments have proved, fay thefe philofopliers, 

 that it is not the light of the day that opens the leaves of this 

 plant, nor the darknefs of the night that doles them ; neither 

 is it the alternate warmth of the day and cold of the night, 

 tliat have this effeft, fince it (huts in nights which are much 

 warmer than the days often are in which it opens ; and the 

 increafihg the heat of the place in which it is kept, and mark- 

 ing the increafe ur decreafe on the thermometer, have been 

 found to have not the le:ift effeft, as to its fooner or later 

 opening or (hutting its leaves. 



The m )it proDabt ■ conjefture feems, that it is not great 

 heat, or ^'reat ccld, fuch as it can bear, that bring on 

 this I ff <S, but the fudden change from one to the other, and 

 thi", is ci nhrmed by this experiment, that if one of thefe 

 plants be raifed under a glafs bell, or cafe, and the bell or 

 covering be takei: otl, It immediately clofes, even though it 

 be in the middle of the day ; and this is alfo obferved, that 

 the m'-re open or expofed the plant ftands, the more (trong 

 and lively are its (hutting and opening ; and that they are 

 mo.l obfervable in furamer, and much lefs fo when it is kept 

 in a clofe (love in winter. 



The great heats of fummer, when there is open fun(hine at 

 noon, allcct the plant in fome degree like cold, caufing it to 



2 (hut 



