CLIMBING PLANTS. 695 



stalk, whilst the latter, after the laminae are unfolded, curve like an arch, forming 

 an actual loop. 



As already stated, no distinction can be recognized in the earlier stages between 

 interweaving stems and those with ringed tendrils. The difference first appears as 

 soon as the lower side of the leaf-stalks comes in contact with a branch of the 

 undergrowth. This contact, if it is not of too transient duration, acts as a stimulus 

 on the leaf -stalk, and the result is that it curves round the branch and grips it like a 

 ring. The stalks always curve towards the side which has been touched, or pressed. 

 Since the leaf-stalks are equally sensitive on all sides, the curvature may take place 

 above or below, or laterally, according to whichever part has been stimulated. Even 

 continuous contact with flower-stalks of hair-like delicacy is sufficient to produce 

 the ring- formation, and it has been shown by experiment that the continued pressure 

 of a thread weighted up to four milligrams is followed by a curvature. The stimu- 

 lated leaf -stalk usually forms one or two, less often several annular coils on the 

 branch embraced, as shown in fig. 163. It also frequently happens that neighbour- 

 ing stems of the same plant are connected together by their tendrils and twined 

 into inextricable knots. The conversion of the irritable leaf -stalk into an effective, 

 gripping tendril in many of the plants in this group is materially assisted by the 

 fact that the younger portions of the shoot revolve in circles like those of twining 

 stems, though less regularly. Thus a much-increased number of suitable objects in 

 the environment become possible as supports. These leaf -stalks, which become 

 tendrils, do not, however, themselves nutate, consequently they are clearly dis- 

 tinguished from those of the following group, which are called nutating tendrils. 



Stems with nutating tendrils have not the power of climbing up rocky walls 

 or the bark of thick tree-trunks, and, like the foregoing, are only able to use as 

 supports culms, leaves, and thin branches of other erect plants, to which they adhere 

 and up which they are drawn by means of the spiral curvature of the attached 

 tendrils. Plants equipped with this class of tendril require far more light than 

 those with ringed tendrils, and they find their best and most favourable habitat in 

 the open country dotted with isolated groups of trees, or on the edges of a forest 

 bordered with bushes, and in sunny meadows studded with shrubs. They have not 

 to interweave through the interlacing branches of an underwood; ringed tendrils 

 are suitable there, but not tendrils with long nutating filaments which could either 

 not accomplish their movements in the midst of the thick brushwood, or if they did, 

 would not attain the desired end, viz. the subsequent elevation of the stem. 



The lowest portions of the young shoot possess no tendrils, and they are kept 

 erect solely by the turgescence of their tissues. In many species the stiff, spreading 

 leaf -stalks, or the peculiar barbed leaf-blades help to support the young shoots on 

 the neighbouring plants and to keep them erect. But these supports are but tem- 

 porary measures, and the upper portion of the shoot soon develops tendrils. These 

 elongate quickly and get to work. The filaments of these tendrils elongate with 

 extraordinary rapidity, straighten out, and then project like tentacles far beyond 

 the foliage-leaves. At their tips only do they exhibit a more or less hook-like 



