52 MORPHOLOGY OF STEMS. 



b} r coiling in the opposite direction, as the Bean (Phaseolus) , 

 the wood}' Aristolochia Sipho, the Morning Glory (Fig. 91") and 



other Convolvu- 

 laceae. The Dod- 

 der, a leafless par- 

 asitic plant of the 



latter family, not cnly gains suppoit .by coiling 

 on the stems of other plants, but by attachment, 

 through the development of sucker-like discs, 

 along the whole contiguous surface. (Fig. 77.) 

 The various actions through which plants climb, 

 and the attendant phenomena, are physiological, 

 and will be treated in the second part of this 

 Text Book. The most complete and satisfac- 

 tory discussion of the subject, of a readable sort, 

 is that of Darwin's volume, referred to in a 

 910 preceding note. 



101. Leaf- Climbers are those in which support is gained by the 

 action, not of the stem itself, but of the leaves it bears ; in most 

 by the coiling or clasping of petioles, as in Clematis, Maurandia, 

 Tropaeolum, and Solanum jasminoides (Fig. 235) ; in some by 

 the incurvation of leaf-blades or portions of them, as in Adlu- 

 mia ; or by an extension of the midrib into a hook or short ten- 

 dril, as in Gloriosa ; or by the transformation of some of the 

 blades of a compound leaf into hooks or tendrils, as in Cobaea 

 and the Pea. 



102. Tendril-Climbers (Fig. 92-95) are those in which the 

 prehension is b}* a tendril, a slender filiform bod}', either simple 

 or branched, specially adapted to the purpose, and capable of 

 coiling, either to secure a hold, or to draw the stem up to the 



coil or circle from the inside ; Mohl, Palm, Braun, and the DeCandolles 

 adopt this, and the latter insist on it. Such authority should be decisive, 

 if common usage and popular sense went along with it. But some of the 

 botanists following Linnaeus adopted the reverse view; and to the present 

 writer, as to Bentham and Hooker, Darwin, Eichler, and in part G. Henslow, 

 it was so natural to view the coil from the outside that we without concert 

 adopted this position and mode of expression. A right-hand coil, or one 

 turning to the right, with us, is one the turns of which pass from the left to 

 right of a bystander who confronts the coil. It is in this sense that a com- 

 mon screw is called a right-handed screw, and that the right bank of a river 

 is that to the right of the person who follows the course of the stream. So 

 natural is this, that even on a map or plate, which has face and back, and 

 therefore a right and left of its own, the figures occupying its right or left 

 portions are understood to be those which are toward the right or the left 

 hand of the observer who stands before it. 



FIG. 91 a . Dcxtrorsely twining stem of Morning Glory, Ipomoea purpurea. 



