TEKDIUL-BEARERS. 05 



thick or thin branches were tossed to and fro by tlie wind, tlie 

 attached tendrils, had they not been excessively elastic, would 

 instantly have been torn oif and the plant thrown prostrate. But 

 as it was, the Bryony safely rode out the gale, like a ship with 

 two anchors down, and with a long range of cable ahead to serve 

 as a spring as she surges to the storm. 



With respect to the exciting cause of tlie spiral contraction, 

 little can be said. After reading Prof, Oliver's interesting paper * 

 on the hygroscopic contraction of legumes, I allowed a number of 

 different kinds of tendrils to dry slowly, but no spiral contraction 

 ensued ; nor did this occur with the tendrils of the Bryony when 

 placed in water, diluted alcohol, and syrup of sugar. We know 

 that the act of clasping a support leads to a change in the 

 nature of their tissues ; and we call this a vital action, and so 

 we must call the spiral contraction. The contraction is not 

 related to the spontaneous revolving power, for it occurs in ten- 

 drils, such as those of Lathyrus grandiflorus and Ampelopsis 

 hederacea, which do not revolve. It is not necessarily related 

 to the curling of the tips round a support, as we see in the 

 case of the Ampelopsis and Bignonla capreolata^ in which the 

 development of the adherent disks suffices to induce the con- 

 traction. Yet it certainly seems to stand in some close relation 

 to the curling or clasping movement due to contact with a 

 support ; for not only does it soon follow this act, but the spiral 

 contraction generally begins close to the curled extremity, and 

 travels down towards the base, as if the whole tendril triedto imitate 

 the movement of its extremity. If, however, a tendril be very 

 slack, the whole length seems to become almost simultaneously 

 at first flexuous and then spiral. The spiral contraction of a 

 tendril when unattached cannot serve any of the useful ends 

 just described ; it does not occur with many kinds of tendrils 

 which contract when attached ; and when it does occur, it super- 

 venes, as we have seen, only after a considerable inten^al of time. 

 It may almost be likened to certain instinctive or habitual move- 

 ments performed by animals under circumstances rendering them 

 manifestly useless. 



When an uncaught tendril contracts spirally, the spire always 

 runs in the same direction from tip to base. A tendril, on the 

 other hand, which has caught a support by its extremity, inva- 

 riably becomes twisted in one part in one direction, and in another 

 part in the opposite direction ; the oppositely turned spires being 



* Trans. Linn. Soc. vol. x^v. 1864, p. 415, 



