642 THE POPULAR SCIENCE MONTHLY. 



it, the plant discovers that it has heen deceived, and, after bending for 

 a time, it unbends and becomes straight again. 



The bending, which enables a leaf to seize a twig, is not the only 

 change which the stimulus of a touch produces. The leaf -stalk swells 

 and becomes thicker and more woody, and turns into a strong, perma- 

 nent support to the plant. The thickening of the leaf -stalks is to be 

 made out in Fig. 2, which represents a shoot of clematis, bearing two 

 leaves, each of which has seized a twig ; in one of the leaf-stalks this 

 thickening has commenced, and is fairly evident. The thickened and 

 woody leaf -stalks remain in winter after the leafy part has dropped 

 off, and in this condition they are strikingly like real tendrils. 



The genus Tropoeolum, whose cultivated species are often called 

 nasturtiums, also consists of leaf-climbing plants, which climb like 

 clematis by grasping neighboring objects with their leaf -stalks. 



In some species of Tropwolum we find climbing organs developed, 

 which can not logically be distinguished from tendrils ; they consist of 

 little filaments, not green like a leaf, but colored like the stem. Their 

 tips are a little flattened and furrowed, but never develop into leaves ; 

 and these filaments are sensitive to a touch, and bend toward a touch- 

 ing object, which they clasp securely. Filaments of this kind are 

 borne by the young plant, but it subsequently produces filaments with 

 slightly enlarged ends, then with rudimentary or dwarfed leaves, and 

 finally with full-sized leaves ; when these are developed they clasp 

 with their leaf-stalks, and then the first-formed filaments wither and 

 die off ; thus the plant, which in its youth was a tendril-climber, grad- 

 ually develops into a true leaf -climber. During the transition, every 

 gradation between a leaf and a tendril may be seen on the same plant. 



It is not always the stalk of a leaf which is 

 developed into the clasping organ ; the bignonia- 

 leaf shown in Fig. 3 bears tendrils at its free ex- 

 tremity. And in other plants tendrils are formed 

 from flower-stalks, in which the flowers are not 

 developed, or the whole stem of the plant or a 

 single branch may turn into a tendril. In one 

 curious case of monstrosity, what should have 

 j W^ been a prickle on a sort of cucumber, grew out 



fig. 3. Biononia. An un- into a long, curled tendril. 



named species from Kew. Tbe f amily Q f the BigilOn ICIS is Olie of the most 



interesting of the class of tendril-climbers, on account of the variety 

 of adaptation which is found among them. 



In the above-mentioned Fig. 3 is seen the tendril-bearing leaf of 

 a species of Bignonia. The leaf bears a pair of leaflets, and ends in a 

 tendril having three branches. The main tendril may be compared 

 to a bird's leg with three toes, each bearing a small claw. And this 

 comparison seems apt enough, for, when the tendril comes against a 

 twig, the three toes curl round it like those of a perching bird. 



