If a terminal subleaflet be pinched with forceps, or cut with scissors, it rises, together with its fellow; then the next pair rise; then the next; and so on in succession, till all the pairs of subleaflets upon the same subpetiole are folded. In a little time afterwards, the petiole is bent downwards at its intumescence; and in a few seconds more the remaining leaflets upon the same petiole fold their subleaflets in pairs, from the base towards the point of the leaflet. [Illustration: _Fig._ 2.] If a subleaflet be burnt, instead of being cut or pinched, the phenomena above described occur more rapidly: and after they have taken place, the adjoining leaves upon the same branch are bent down in succession, their leaflets brought together, and their subleaflets folded. If the plant be very vigorous and lively, an impression [p079] made upon one leaf affects the rest in succession. It is well known that the stem, branches, flowers, and roots of the sensitive plant have no motion. But M. Desfontaines observed that, on touching the roots with sulphuric acid, the leaves become folded; and M. Dutrochet obtained a similar result on burning either the flower or the stem. [Illustration: _Fig._ 3.] [Illustration: _Fig._ 4.] [Illustration: _Fig._ 5.] If the plant be shaken, all the leaves are simultaneously thrown down, and their leaflets folded. Mr. Lindsay attempted to elucidate the action of the intumescence in raising and depressing the petiole, in the following manner. He cut out a portion from the upper or solar surface of the intumescence; after which he found that the petiole, upon recovering, rose higher than before, (_Fig._ 3.) From another leaf he removed the inferior portion of the intumescence: he found, upon _this_ injury, that the leaf declined more than before, and did not again rise, (_Fig._ 4.) He noticed that a thin slice, pared from either surface of the intumescence, has a like effect, but in a less degree than a deep excision: and he found that when similar experiments are made upon the intumescence of the subpetiole, there is no essential difference in the result. Thus Mr. Lindsay discovered, that the force which raises the petiole exists in the lower part of the intumescence, and that which depresses it, in the upper. He seems to have considered that the temporary excess of force in either part is produced by an impulsion of the sap from the vessels of the yielding portion into those of the opposite portion. [p080]