Chap. II. LEAF-CLIMBEKS. 83 



seize distant objects. The petioles of the perfect 

 leaves of Tropseolum tricolorum, as well as the tendril- 

 like filaments of the plants whilst young, ultimately 

 move towards the stem or the supporting stick, which 

 they then clasp. These petioles and filaments also 

 show some tendency to contract spirally. The tips of 

 the uncaught leaves of the Gloriosa, as they grow old, 

 contract into a flat spire or helix. These several facts 

 are interesting in relation to true tendrils. 



With leaf climbers, as with twining plants, the first 

 internodes which rise from the ground do not, at least 

 in the cases observed by me, spontaneously revolve ; 

 nor are the petioles or tips of the first-formed leaves 

 sensitive. In certain species of Clematis, the large size 

 of the leaves, together with their habit of revolving, 

 and the extreme sensitiveness of their petioles, appear 

 to render the revolving movement of the internodes 

 superfluous; and this latter power has consequently 

 become much enfeebled. In certain species of Tro- 

 pseolum, both the spontaneous movements of the inter- 

 nodes and the sensitiveness of the petioles have become 

 much enfeebled, and in one species have been com- 

 pletely lost. 



