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In those plants in which the terminal shoot is not sufficiently out of the way, as we have seen with the Echinocystis, as soon as the tendril comes in its revolving course to this point, it stiffens and straightens itself, and thus rising vertically up passes over the obstacle in an admirable manner.
In the Echinocystis I have seen a tendril with the two lateral branches encircling twigs and contracted into beautiful spires, whilst the main branch which had caught nothing remained for many days straight. In this plant I once observed a main branch after it had caught a stick become spirally flexuous in 7 hrs., and spirally contracted in 18 hrs.
Berkeley thinks that Payer's view is the most probable, namely, that the tendril is "a separate portion of the leaf itself;" but much may be said in favour of the belief that it is a modified flower-peduncle. Echinocystis lobata. My observations may now be much condensed.
But in Cobaea and Passiflora punctata the tendrils begin to revolve in a useless manner, before they have become sensitive. In the Echinocystis they retain their sensitiveness for some time after they have ceased to revolve and after they have sunk downwards; in this position, even if they were able to seize an object, such power would be of no service in supporting the stem.
The clasping movement of the extremity is apparently not steady, but undulatory or vermicular in its nature, as may be inferred from the curious manner in which the tendrils of the Echinocystis slowly crawled round a smooth stick.
The tendrils of the Echinocystis are also habituated to drops of water or to rain; for artificial rain made by violently flirting a wet brush over them produced not the least effect. The revolving movement of a tendril is not stopped by the curving of its extremity after it has been touched. When one of the lateral branches has firmly clasped an object, the middle branch continues to revolve.
CUCURBITACEAE. Homologous nature of the tendrils Echinocystis lobata, remarkable movements of the tendrils to avoid seizing the terminal shoot Tendrils not excited by contact with another tendril or by drops of water Undulatory movement of the extremity of the tendril Hanburya, adherent discs VITACAE Gradation between the flower-peduncles and tendrils of the vine Tendrils of the Virginian Creeper turn from the light, and, after contact, develop adhesive discs SAPINDACEAE PASSIFLORACEAE Passiflora gracilis Rapid revolving movement and sensitiveness of the tendrils Not sensitive to the contact of other tendrils or of drops of water Spiral contraction of tendrils Summary on the nature and action of tendrils.
Generally the tendrils of the Echinocystis begin to contract in from 12 hrs. to 24 hrs. after catching some object; whilst unattached tendrils do not begin to contract until two or three or even more days after all revolving movement has ceased.
It was hardly necessary to observe this fact; but I did so by affixing little paper vanes to the extreme points of the tendrils of Echinocystis and Passiflora quadrangularis; and as the tendril contracted itself into successive spires, the vane slowly revolved.
I repeated the experiment made on the Echinocystis, and placed several plants of this Passiflora so close together, that their tendrils were repeatedly dragged over each other; but no curvature ensued. I likewise repeatedly flirted small drops of water from a brush on many tendrils, and syringed others so violently that the whole tendril was dashed about, but they never became curved.
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