. The origin of floral structures : through insect and other agencies. Plants; Flowers; Flowers. 152 THE STEUCTUBE OF or mectanical irritations. Thus Fig. 45* shows the effect of electrical action on the threads of protoplasm; a represents a cell of a hair of Tradescaniia Tirgi- niaca; b the same, after the application of an electrical cnrrent. The following are Dr. Weiss's observations upon this phenomenon:— " A constant electrical current is without influence upon the protoplasmic excitation; whereas the alternate shocks f * From Weiss's Anatomie der. PJlanzen, p. 95. t PfefEe
. The origin of floral structures : through insect and other agencies. Plants; Flowers; Flowers. 152 THE STEUCTUBE OF or mectanical irritations. Thus Fig. 45* shows the effect of electrical action on the threads of protoplasm; a represents a cell of a hair of Tradescaniia Tirgi- niaca; b the same, after the application of an electrical cnrrent. The following are Dr. Weiss's observations upon this phenomenon:— " A constant electrical current is without influence upon the protoplasmic excitation; whereas the alternate shocks f * From Weiss's Anatomie der. PJlanzen, p. 95. t PfefEer has noticed that the weight, per se, ^'fJ^i^^^Z^ Zn. Of the body in contact [if very slight?] is of dition; b, under electrical no consequence to tendrils. Thus cotton-wool action (after Weiss). .^eighing -00025 grain produced no effect if caxefnlly placed on them; but it did when a gentle impact was caused by slight currents of air. Tentacles of Drosera have a sensitiveness very similar to that of tendrils, inasmuch as small splinters of glass only produced irritation of the glands when they caused a rubbing as the result of concussion (see Journ. Boy. Micr. Soc, 1886, p. 285). PfefEer concludes that the conduction of sensitiveness is not alto- gether due to a continuity of protoplasm, as it does not extend to the epidermis. Since, however, the outer cell-wall of the epidermis can grow when in contact with a foreign body, it wonld seem to clearly indicate that under such circumstances it still retained its protoplasm; and that the modem view of the cell-wall being at first a protoplasmic layer, and not altogether a dead secretion from the protoplasm within it, is correct; for otherwise it is difficult to imagine how it could adapt itself to the surfaces of foreign objects at all. Heckel, in studying the movements of the stamens in SparmaTvnia, Cistiis, and Melianthenmm, discovered that the epidermis plays an important part: " L'epiderme, contrairement k oe que voulait
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