. Un texte-livre de botanique pour les écoles secondaires. La botanique. 48 UN TEXTE-LIVRE OP botanique dans d'autres cas, comme la vigne et star-concombre, vrilles, qui ou ficelle hooli sur les supports (Fig. 48) ; dans d'autres cas encore, comme l'hippodrome Woodbine, les vrilles pro- -^ duce drageons qui agissent comme crampons et permettre à la plante de s'accrocher aux arbres ou murs (Fig. 49 et 50). C'est dans les forêts denses tropicales que grimper des plantes deviennent particulièrement remarquable. Il y a beaucoup de la vigne des entrelacs assez la végétation, et sont connus comme des lianes ou liancx. Si un jeune matin- gloire ou twining bean b

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. A text-book of botany for secondary schools. Botany. 48 A TEXT-BOOK OP BOTANY in other cases, as the grape-vine and star-cucumber, tendrils are formed, which twine or hooli about the supports (Fig. 48); in still other cases, as the woodbine, the tendrils pro- -^ duce suckers that act as holdfasts and enable the plant to cling to trees or walls (Figs. 49 and 50). It is in the dense forests of the tropics that climb- ing plants become espe- cially conspicuous. There great woody vines fairly interlace the vegetation, and are known as lianas or liancx. If a young morning- glory or twining bean be watched, it will be dis- covered that the elonga- ting stem is unable to stand upright, and that, as it bends over, the inclined part begins to swing through a horizontal curve, which may bring the stem in contact with a suitable support. If this hap- pens, the stem, continuing to swing in a curve and growing in length at the same time, winds itself about the support. This movement of the portion of the stem which is in a hori- zontal position is thought to be brought about by a peculiar response of the plant to gravity. The influence of gravity in directing plant organs will be considered later. Tendrils are illustrations of plant structures that are unusually sensitive to contact. When the tip of a tendril in moving aljout touches a suitable support, the side touched becomes concave and the tendril hooks or coils about the support. This is only the first response of the tendril to contact, for presently the rest of it begins to cur^•e—a move-. FlG. 48.—Branch of star-cucumber, with its tendrils in various conditions.. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original work.. Coulter, John Merle, 1851-1928. New York, D. Appleton

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