TWINERS AND OTHER CLIMBING PLANTS 



277 



If a twining plant is placed upon a clinostat and slowly rotated about a 

 horizontal axis, the twining movement ceases and growth proceeds in a direc- 

 tion parallel to the axis of rotation, while the younger turns of the previously- 

 formed spiral become straightened out. Such experiments indicate that a 

 geotropic response is necessary for twining. 



§2. Non-twining Climbers.^ — The long stems of non-twining climbers are 

 unable to twine, but they climb by means of hairs, thorns, aerial roots, tendrils, 



6^ c 



Fig. 153. — Twining stem of Humulus lupulus, in 

 successive stages of movement. {After Pfeffer.) 



A B 



Pig. 154. — A. Pharbitis, shoot 

 showing counter-clockwise twining. 

 B. Myrsiphyllum asparagoides', shoot 

 showing clockwise twining. {After 

 Bonnier.) 



etc. Tendrils are the most frequent of these special structures. These are 

 morphologicaUy different in different plants; in some forms (Vitis, Ampelopsis, 

 the Cucurbitacese) they correspond to twigs, while in others they are leaves; 

 thus the upper part of the pea leaf is a tendril while the pinnately arranged leai- 

 lets of the lower part are quite like those of ordinary leaves. 



' Daiwin, Charles, 1875. [See note i, p. 276.] Vries, Hugo de, L&ngenwachsthum der Ober-und Ua- 

 teiseite-sich kriimmenderJlanken. Arbeit. BotJost.-Warabutg,l: 302-316. 1874. Schenck, Heiniich, 

 Beitr&ge zur Biologie und Anatomie der Lianen im besonderen der in Brasilien einheimischen Arten. 2 v. 

 Jena, 1892-1893. (Lengerkin, August von, Die Bildung der Haftballen an den Ranken einiger Arten der 

 Gattung Ampelopsis. Bot. Zeitg. 43: 337-346. 3S3-36i,369-j79. 385-393. 40I-4". i88s. MacDougal, 

 D. T., Mechanism of the curvature of tendrils. Ann. bot. 10: 373-402. 1896. Idem, 1901. (See 

 note I, p. 276.) Pringsheim, 191a. (See note i, p. 223.)] 



