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Show 254 DHOSERA ROTUNDIFOLIA. CHAP. X. ]fechanism of the Movements, and Nat-ure of the Motor Impulse.-Whatever may be the I~eans of movement, the exterior tentacles, considering their delicacy, are inflected with much force. A bristle, held so that a length of 1 inch projected from a handle, yielded when I tried to lift with it an inflected tentacle, which was somewhat thinner than the bristle. The amount or extent, also, of the 1novement is great. Fully expanded tentacles in beco1ning inflected sweep through an angle of 180°; and if they are beforehand reflexed, as often occurs, the angle is considerably greater. It is probably the superficial cells at the bending place which chiefly or exclusively contract; for the interior cells have very delicate walls, and are so few in number that they could hardly cause a tentacle to bend with precision to a definite point. Though I carefully looked, I could never detect any wrinkling of the surface at the bending place, even in the case of a tentacle abnormally curved into a co1nplete · circle, under circu1nstances hereafter to be mentioned. All the cells are not acted on, though the motor impulse passes through them. When the gland of one of the long exterior tentacles is excited, the upper cells are not in the least affected; about halfway down there is a slight bending, but the chief movement is confined to a short space near the base; and no part of the inner tentacles bends except the basal portion. vVith respect to the blade of the leaf, the motor i1npulse may be transmitted through many cells, from the centre . to the circumference, without their being in the least affected, or they may be strongly acted on and the blade greatly inflected. In the latter case the movement seems to depend partly on the strength of the stimulus, and partly on CHAP. X. MEANS OF MOVEMENT. 255 its nature, as when leaves are immersed in certain fluids. The. P?wer of movement which various plants possess, when unt~ted, has been attributed by high authorities to the rap1d passage of fluid out of certain cells which from their previous state of tension, immediat~ly con~ tract.* Whether or not this is the primary cause of such movements, fluid must pass out of closed cells when they contract or are pressed toO'ether in one direction, u~less. they at t.he same ti~e expand in some other duect1on. For Instance, fluid can be seen to ooz~ from the surface of any young and vigorous .shoot If slowly bent into a semi-circle.t In the case of Drosera there is certainly much movement of the flu~d t~roug~out the tentacles whilst they are undergoing Inflection. Many leaves can be found in which t~e purple fluid within the cells is of an equally dark tint on the upper and lower sides of the tentacles extendin? also downwards on both sides to equall; near theu bases. If the tentacles of such a leaf are excited into movement, it will generally be found after some hours that the cells on the concave side are much paler than they were before, or are quite colourless those on the convex side having become much darke/ In two instances, after particles of hair had been placed on glands, and when in the course of 1 hr. 10m. the tentacles were incurved halfway towards the centre of the leaf, this change of colour in the two sides was eonspicuously plain. In another case, after a bit of meat had been placed on a gland, the purple colour was observed at intervals to be slowly travelling from the upper to the lower part, down the convex side of ---------- * Sachs, 'Tmite de Bot.' 3rd Lamarck. edit. 1874, p. 1038. 'fhis view t S ac h s, 1'b 1'd • p. 919 . was, I believe, first suggested by |