290 HOTANY PART i 



only produced as the result of contact, and the tendrils of these plants are able 

 also to grasp thin supports. 



Sometimes, as in the case of Lophospermum scundeiis (Fig. 234), the leaf-stalks, 

 although bearing normal leaf- blades, become irritable to contact stimuli and 

 function as tendrils. Of leaf-stalks which thus act as tendrils, good examples are 

 alforded by Tropaeolum, Maurandia, Solanum jasminoides, Nepenthes, etc. The 

 subsequent modifications occurring in more perfectly developed tendrils are not 

 noticeable in the case of petiolar tendrils, although the coiling portion of the leaf- 

 stalk of Solanum jasminoides does become strongly thickened and lignified ; 

 while the leaf-blades of Clematis, by remaining small for a time, enhance the 

 tendril-like character of their leaf-stalks, and by bending backwards also assist in 

 maintaining the initial contact with a support. At other times the midribs of 

 the leaf-blades themselves become prolonged, and assume the function of tendrils 

 (Gloriosa, Littonia, Flagellaria). In many species of Fumaria and Corydalis, in 

 addition to the leaf-stalks, even the leaf-blades of the leaflets twine around slender 

 supports, while the parasitic shoots of Cuscuta (Fig. 186) are adapted for both 

 twining and climbing. Climbing parts of the thallus occur in some Thallophyta 

 (Florideae) ( w ). 



Kic. 1:14.- Loplioxpernnim scandens climbing by means of its tendril-lik** ]'tioles. 



F. Curvatures of Growth due to Variations in Light and Temperature 



The flowers and foliage leaves of many plants exhibit the 

 peculiarity that their different sides (the upper and under sides of 

 foliage-leaves and leaf-stalks, the inner and outer sides of floral leaves) 

 show an unequal growth in response to even transitory and slight 

 variations in temperature and in the intensity of light. Whenever, 

 on account of such variations, the growth of the under side of a leaf 

 exceeds that of the upper side, the whole leaf moves upwards and 



