General physiology; an outline of the science of life . y known. Mimosa,which resembles a small Acacia tree, during the day and while 1 Cf. Verworn (91). STIMULI AND THEIR ACTIONS 381 undisturbed holds its primary petioles, which spring from the trunk,directed obliquely upward. The secondary petioles, which bearthe rows of leaflets, are spread out wide apart, and the leaflets them-selves stand horizontal and widely extended (Fig. 172,^4). But assoon as the pot in which the plant is growing is shaken, the picturechanges almost immediately. The primary petioles fall downas a result of the decrea
General physiology; an outline of the science of life . y known. Mimosa,which resembles a small Acacia tree, during the day and while 1 Cf. Verworn (91). STIMULI AND THEIR ACTIONS 381 undisturbed holds its primary petioles, which spring from the trunk,directed obliquely upward. The secondary petioles, which bearthe rows of leaflets, are spread out wide apart, and the leaflets them-selves stand horizontal and widely extended (Fig. 172,^4). But assoon as the pot in which the plant is growing is shaken, the picturechanges almost immediately. The primary petioles fall downas a result of the decrease of the turgor of the cells of theirpulvini, the secondary petioles turn toward each other, while the leaf-lets are raised and lie with their upper surfaces together (Fig. 172, B).The plant, when left at rest, remains for some time in this position,and then very gradually returns to its original condition, the cell-turgor again increasing at the corresponding portions of the the single leaflet the position of stimulation can be called out. Fig. 172.—Mimosa pudica. A, A branch unstimulated and extended ; Ji, a branch stimulatedand fallen, with its leaves folded. (After Detmer.) also by a very gentle local touch. If the touch be stronger, theleaflets may be seen to move in succession like a row of dominoes,thus affording a very striking demonstration of the transmissionof the stimulus. Among the contraction-movements resulting from the mechanicalstimuli the contraction-phase only is thus far recognised withcertainty, although it is not improbable that in many cases verydelicate tactile stimuli may produce expansion. Thus, the contactof an amoeboid protoplasmic mass with a smooth support mightinfluence by cohesion the extension of the pseudopodia. In the naked protoplasmic bodies of Bhizopoda a single shock uponthe extended pseudopodia, such as can be produced by a vigorousrap of the slide under the microscope, produces more or less pro- 382 GENERAL PHYSIOLOGY nounc
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