Lectures on the physiology of plants . exert on the support,those cases are very instructive where thin leaves are entwined by strong tendrils, andare thereby compressed and folded. Since the biological object of tendrils is to grasp supports—usually otherplants—and thus to enable the thin stems of the tendril-plant to climb, itbecomes a matter of primary importance to bring the tendrils into contact withsupports; this is usually accomplished in a wonderfully complete manner by thefact that at the time when they are irritable, not only the tendrils themselves but alsothe apex of the shoot whic
Lectures on the physiology of plants . exert on the support,those cases are very instructive where thin leaves are entwined by strong tendrils, andare thereby compressed and folded. Since the biological object of tendrils is to grasp supports—usually otherplants—and thus to enable the thin stems of the tendril-plant to climb, itbecomes a matter of primary importance to bring the tendrils into contact withsupports; this is usually accomplished in a wonderfully complete manner by thefact that at the time when they are irritable, not only the tendrils themselves but alsothe apex of the shoot which bears them are endowed with revolving nutation, withthe result that every object which can be used as a support, and which is by any BIOLOGICAL ADAPTATIONS OF TENDRILS. 667 means brought wiihin tlie area swept by the tendrils, almost certainly comes in contactwith one. The apex of the shoot bearing the tendrils usually describes elliptical ascend-ing spirals, the course of which is completed in from i to 5 hours. As with twining. ^-^^^^^ -r ^-_ ^- -^)); FIG. 378,—Upper portion of the end of a climbing shoot of the Virginian Creeper [Ampelopsis heiUtacea). h a tendrilwhich has coiled itself in the ordinary manner round a nail; a c tendrils which have become fixed to the wall by means ofcushion-like outgrowths or clasping organs; d a tendril which is still nutating—its tips are groping about on the wall, butare still devoid of clasping organs ; e young tendrils. Stems so also with tendrils, a pronounced positive heliotropism would often carry themaway from the support, and would therefore be injurious. Some in fact appear to benot heliotropic at all {Pisiim according to Darwin), in others a feeble positive helio-tropism makes itself evident by the fact that the circular nutating movement takesjilace more quickly towards the light than away from it. Some tendrils, particularly 668 LECTURE XXXVIII. those of Ampelopsis hederacea (the Virginian Creeper), and Bignoina capreo
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectplantph, bookyear1887
