698 CLIMBING PLANTS. 



bears a double claw whose points immediately fasten into any object at the slightest 

 touch, and will even remain suspended in the skin of the hand. The three delicate 

 branches of the tendril of Bignonia venusta also end in pointed claws which 

 resemble those of insects' feet. The majority of tendrils are branched, whilst simple 

 undivided filaments, as shown in the Bryonia (fig. 165), are comparatively rare. 

 Passion-flowers and gourd-plants have the longest tendrils, those of the common 

 gourd (Gucurbita pepo) often measuring more than 30 cm. in length. The spiral 

 contraction of the part of the tendril not wound round the support begins, according 

 to the species, half a day, or one or two days after the apex has formed the first 

 coil round the support, but it is very quickly accomplished when it has once begun. 

 This torsion is sometimes towards the right, sometimes towards the left, and fre- 

 quently it is accomplished partly in one direction and partly in the other, by the 

 same tendril. The number of twists formed in this spiral contraction is very vari- 

 able. In the long tendrils of some gourds as many as 30 or 40 are produced. By 

 these spiral springs the fastening of the stem to the support is excellently accom- 

 plished ; it is at once adequately attached to the support, but not pressed to it, conse- 

 quently unnecessary friction is avoided. During a blast of wind there is a certain 

 amount of "give", but directly the gust subsides, the climber — thanks to its elastic 

 tendrils — resumes its former position. This spiral twisting occurs also in tendrils 

 which have not succeeded in grasping a support, but strangely enough, they become 

 stunted, shrivel, and wither, sometimes becoming detached from the stem like 

 autumn leaves. Those tendrils, on the other hand, which have embraced a 

 support become much stronger and thicker, and also undergo a series of changes 

 in their inner structure which adapt them excellently to the part they have to 

 perform. 



Stems with light-avoiding tendrils remind us of the light-avoiding interweaving 

 and lattice-forming stems, and, like these, are found in plants which have to climb 

 up steep rock faces and over the bark of large trees. In these cases the more or 

 less plane surface of the rock or tree-trunk is the only support afforded for climb- 

 ing. The stem on such a substratum would extend its tendrils in vain on the side 

 where there is only the air to be met with; here there is no resting-place or 

 support which can be reached by circling movements. The best the tendril can do 

 under the circumstances is to seek out the solid wall along which the stem has to 

 climb as quickly as possible. In such cases the desired support is on the side 

 turned away from the light, and as a matter of fact, the tendrils of these plants 

 turn towards this side with great persistence. According to the position of the 

 point at which the tendril springs from the stem, it curves at an angle of 90-180° 

 in less than 24 hours, and grows towards the background without digression and 

 without wasting its energy in revolving movements. The leaves of the same plant, 

 for exposure to light and air, are extended in a direction away from the wall, and 

 try to assume the position most favourable for this purpose. The path it has taken 

 soon brings the tendril in direct contact with the wall, with which it now has to 

 obtain a firm hold. This it does either by peculiar adhesive discs, or by wedging itself 



