. Plant physiology. Plant physiology. 278 PHYSIOLOGY OF GROWTH AND CONFIGURATION Young, actively growing tendrils nutate, so as to beconie hook-shaped. When the tendril comes into contact with a solid object coiling begins near the tip, so that it wraps itself about the support, if this is of suitable size and shape. This coiling movement results from unequal growth on the two opposite sides, brought about as a response to the stimulus of contact. The portion of the tendril that lies between the point of attachment and the base does not remain permanently straight but subsequently also becomes
. Plant physiology. Plant physiology. 278 PHYSIOLOGY OF GROWTH AND CONFIGURATION Young, actively growing tendrils nutate, so as to beconie hook-shaped. When the tendril comes into contact with a solid object coiling begins near the tip, so that it wraps itself about the support, if this is of suitable size and shape. This coiling movement results from unequal growth on the two opposite sides, brought about as a response to the stimulus of contact. The portion of the tendril that lies between the point of attachment and the base does not remain permanently straight but subsequently also becomes coiled, in the form of a spiral spring, so that the plant is drawn nearer to the support. The stem is thus not supported by a straight-and inelastic suspension, which might be easily broken, but it hangs upon a coiled spring, which stretches a little when the plant is moved by the wind, thus (largely avoiding the possibihty of breaking. Theitendril can become attached to a support only while still growing, and those that have not come into con- tact with a suitable support during the growing period generally wither and fall away. Fig. 155 repiresents a portion of the stem of Bryonia dioica, with a tendril attached to a twig of another plant. The middle portion of the tendril forms the spiral spring mentioned above. ' The tendrils of Ampelopsis behave in a peculiar manner when they' happen to come into contact with an object about which they cannot twine, as in growing along a wall, for example. Some of the tendrils, appressed against the wall by a negative phototropic response and which continually nutate, happen to r6ach into crevices in the support. Such a tendril becomes thickened at the end within the crevice, so that it cannot be readily withdrawn, thus supporting the plant. [These tendrils also form adhering disks at their tips, by which they become attached to nearly smooth surfaces. (Fig. 156.)] Investigations of the anatomy of tendrils show that these posses
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