LECTURE XXXVIII. 



THE REVOLVING OF TENDRILS AND TWINING PLANTS. 



The great majority of sub-aerial leafy shoots are enabled, by means of their 

 rigidity and geotropism, to maintain themselves erect so as to spread their organs 

 of assimilation to the light, to render their flowers visible to the insects which 

 pollinate them, and to mature their fruits and seeds in the air so that they can be 

 easily detached from the parent plant and disseminated by the wind or by animals. 



In very many other plants, on the contrary, the long shoot-axes are too 

 slender and too flexible to be able to maintain themselves in this upright position 

 beneath the weight of the organs which they support, although as a rule the 

 above advantages accrue to them in proportion to the elevation they attain. They 

 ascend, however, by quite other means — not by simply growing erect, but by 

 climbing. 



The climbing plants, again, differ in their habit of life, and in their modes 

 of climbing. The Blackberry, for example, and the Rattan- or Cane-palms (Calamus) 

 (with stems about as thick as the finger and sometimes too m. long), fling, 

 so to speak, their long shoots on the jungle and on the branches of trees, 

 and hang there by means of their hooks. Much more completely organised, 

 as climbing plants, are the Ivy and others. The long thin shoot-axes of the Ivy 

 apply themselves closely to a wall, the stem of a tree, or a rock, &c., and then grow 

 perfectly erect, or, in the case of lateral shoots, obliquely, on the surface of 

 these supports, and fix themselves by means of numerous small attaching roots 

 to the vertical surfaces on which they are climbing. 



Twining plants are adapted for climbing in an entirely different manner. 

 In these, e. g. the common Hop, species of Bindweed {Convolvulus), &c., the axis 

 of the leaf-shoot, which is at least at first thin and flexible, twines itself 

 around a body which stands vertical or obhquely upright, and is usually thin, 

 such as the trunk of one of the more slender trees, a branch of a shrub, or, in the 

 case of smaller twining plants, such as the common Corn-bind, around the haulms of 

 ordinary grasses, the erect flower-stalks of meadow plants, &c. But it is the tendril- 

 plants which are to be looked upon as the most perfect of all climbing plants, having 

 special organs exclusively adapted for climbing. Moreover, their peculiarities are 

 better known than those of any other climbing plants, and they may therefore be first 

 taken into consideration, 



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