110 GENERAL BOTANY 



they can hardly be said to climb, attach themselves 

 firmly to trees by similar roots. (Epiphytes.) 



The common garden Potato-creeper SOLANUM 

 SEAFORTHIANUM will cling on any thin support, such 

 as a wire, by curving the petiole round it. So also 

 does the garden ' Nasturtium ' (TROP^OLUM) and the 

 Pitcher plant (NEPENTHES), a native of America. In 

 GLORIOSA SUPERBA, common enough in hedges all 

 over South India, the leaves have long extensions 

 which coil round any available object (fig. 22). 



It has been proved that in such cases the coiling 

 is due to the outer side growing more rapidly than 

 the inner, because stimulated to do so by the friction 

 of the object touched. 



In other plants occur special holding organs, called 

 tendrils, which, whatever their morphological nature, 

 are merely thin threads very sensitive to contact with 

 any rough surface, and readily twine round any 

 object. 



If we examine the tendrils of the Vine, ANTIGONON, 

 PASSIFLORA the Passion-flower, Pea, CLEMATIS or any 

 other tendril-climber, we shall find that in every case 

 the fully-formed mature tendril is coiled up like a 

 spring, acting just as a spring in allowing itself to be 

 stretched and contracting again. The direction of the 

 twist of this spiral, it will be noticed, changes one, 

 three or some odd number of times, which shows that 

 the spiral is made after the end has fastened to the 

 support. We have only to tie a piece of string or tape 

 between two points, and twist it up in the middle to 

 see that the direction of the spiral must be different 

 at either end. 



