48 MB. DARWIN OX CUM IUNU PLANTS. 



The young internodes of the Lophospcrmum are sensitive as well 

 as the petioles, and by their combined movement seize any object. 

 The flower-peduncles of the Maurandia sanpei-jlorcns revolve 

 spontaneously, and are sensitive to a touch, yet are certainly use- 

 less for climbing. The leaves of at least two and probably of most 

 of the species of Clematis, and of Fumaria and Adlumia, spon- 

 taneously curve from side to side, like the internodes, and are thus 

 better adapted to seize any distant object. The petioles of the per- 

 fect leaves, as well as the rudimentary or tendril-like leaves of 

 Tropcrolum tricolorum move spontaneously and slowly towards 

 their own stem or the supporting stick, which they then clasp ; 

 these petioles also show some tendency to contract spirally. The 

 tips of the uncaught leaves of the Gloriosa, as they grow old, con- 

 tract into a flat spire. These several facts are interesting, as we 

 shall see, in relation to true tendrils. 



It was observed in some cases that, as with twining plants, so 

 with leaf-climbers, the first internodes which rise from the ground 

 do not spontaneously revolve ; nor are the petioles or tips of the 

 first-formed leaves sensitive. In . certain species of Clematis the 

 high development and spontaneous movements of the leaves, with 

 their highly sensitive petioles, apparently have rendered almost 

 superfluous the spontaneous movements of the internodes, which 

 have consequently become enfeebled. In certain species of Tro- 

 pceolum it would appear as if both the spontaneous movements of 

 the internodes and the sensitiveness of the petioles have become 

 enfeebled ; and in one species they have been completely lost. 



Part III. — Tendril-bearing Plants. 



By tendrils I mean filamentary organs, sensitive to contact and 

 used exclusively for climbing. By this definition, spines or hooks 

 and rootlets, all of which are used for climbing, are excluded. 

 True tendrils are formed by the modification of leaves with 

 their petioles, of flower-peduncles, perhaps also of branches and 

 stipules. Mohl, who includes with true tendrils various organs 

 having a similar external appearance, classes them according to 

 their homological nature, as being modified leaves, flower-pedun- 

 cles, &c. This would be an excellent scheme ; but I observe that 

 botanists, who are capable of judging, are by no means unanimous 

 on the nature of certain tendrils. Consequently I will describe 

 tendril-bearing plants by natural families, following Lindley, 

 and this wdl in most, or in all, cases keep those of the same homo- 



