656 CONSERVATIVE ORGANS. [LECT. XI. 



to you that of petioles and other organs into 

 spines ; and I have now to state that a similar 

 change into tendrils is occasionally observed : as 

 exemplified in the stipules in Smilax. 



The tendril is at first tender, green, and put 

 forth in a straight direction ; but it gradually be- 

 comes firmer in its texture, occasionally acquires 

 colour, and always assumes the spiral character. 

 When all the gyrations are regular in the same 

 direction, the tendril is said to be convolute ( con- 

 volutus); and revolute (revolutus), when it winds 

 itself irregularly, sometimes on one side, some- 

 times on the other. Phytologists have endea- 

 voured to explain the cause of the spirality of 

 tendrils: their opinions, which are by no means 

 conclusive, shall be noticed when we treat of the 

 movements of plants. 



b. The claw (clavicula) is a small thread-like 

 body which is protruded from the stems of some 

 plants ; and adheres so firmly to the surfaces of 

 other bodies, as to enable the plants producing it 

 to elevate themselves from the ground. By means 

 of this description of prop, the Ivy and the 

 Cissus climb not only to the summits of the highest 

 trees, but up the face of the smoothest perpendi- 

 cular rocks, and to the battlements of the loftiest 

 towers; thus rendering picturesque the monotony 

 of the naked cliff, and, by the richness of their 

 living tracery, adding a new interest to the moul- 

 dering pile of antiquity. 



