HOW PLANTS CLIMB. 205 



the flower-stalks. In the latter case the reason is hard to find. 



since no use is made of this property for climbing purposes. 



Four families exhibit the power of climbing by their produced 

 mid-ribs, or tips. 



Two notable cases are Gloriosa, a genus of Liliacece, and 

 Nepe7ithes, the Pitcher-plant. 



In Gloriosa, the tip of the leaf grows into a ribbon-like pro- 

 jection, which gradually coils down into a well-formed hook. 

 Only the inner or under surface in this case is sensitive to 

 touch. If the hook becomes coiled into a ring it loses its sensi- 

 tiveness entirely. When very young the plant can support itself, 

 and no hooks are developed ; when it has done growing the 

 sensitiveness vanishes. In neither case are the hooks needed ; 

 therefore, they are either absent or their sensitiveness departs. 



In Nepenthes, the curled tip of the leaf is used both for climb- 

 ing by, and as a support for, the pitcher. The coiled portion in 

 the latter case is, nevertheless, thickened by way of providing 

 additional strength. 



B. — Tendril-Bearers. 



These are plants having true tendrils — i.e., thread-like sensitive 

 organs, which are used exclusively for climbing. We do not in 

 this definition include spines, hooks, or rootlets. 



Tendrils may be modifications oi petioles, leaves (or portions of 

 leaves), flower- stalks, or stipules. Sometimes the branches are so 

 modified as to become tendrils. In some cases authorities are in 

 dispute over the homological nature of certain tendrils. These 

 we shall do wisely to let alone, confining our remarks to such 

 tendrils as those whose homology is pretty clearly made out. 



I can only in such a paper as this give the merest outline of 

 the facts and functions of tendril life — a sketch of the more 

 prominent and interesting points, referring the reader to pages 

 84 — 182 in Darwin's book for fuller detail, pages well worth 

 diligent study and verification. 



I. — Tendrils wJiich are modified Petioles. 



Of these a good example is that of Lathyrus, the Yellow 

 Vetchling. There are no true leaves, their places being function- 

 ally supplied by large stipules. The petiole, or perhaps this and 

 the mid-rib as well, is converted into a true tendril, sensitive 



