TENDKIL-BEAREKS. 49 



logical nature together ; but I shall treat of each family, one 

 after the other, according to convenience*. The species to be 

 described belong to ten families, and will be given in the following 

 order: — Bignoniacece, Polemoniaccce, Leguminosce, Composites, Smi- 

 lacece, FumariacecB, CucurUtacecc, Vitacece, Sapindacece, Passijlo- 

 raceae. 



Bionontace.'-e. — This family contains many tendril-bearers, some 

 twiners, and some root-climbers. The tendrils are always modified 

 leaves. Nine species of Bignonia, selected by hazard, are here 

 described, in order to show what diversity of structure and action 

 there may be in species of the same genus, and to show how re- 

 markable the action of the tendrils may be in some cases. The 

 species, taken together, afford connecting links between twiners, 

 leaf-climbers, tendril-bearers, and root-climbers. 



Bignonia (an unnamed species from Kew, closely allied to B. 

 unguis, but with smaller and rather broader 

 leaves). — A young shoot from a cut-down Fig. 5f. 



plant made three revolutions against the 

 sun, at an average rate of 2 h. 6 m. The 

 stem is thin and flexible and twined, as- 

 cending, from left to right, round a slender 

 vertical stick as perfectly and as regularly 

 as any true twining-plant. When thus 

 ascending, it makes no use of its tendrils 

 or its petioles ; but when it twined round 



a rather thick stick, and its petioles were 



, , , . , ... ., * . Bignonia, unnamed 



brought into contact with it, these curved species from Kew. 



round the stfiek, showing that they have 



some degree of irritability. The petioles also exhibit a slight 



* As far as I can make out, the history of our knowledge on tendrils is as 

 follows :— Wc have seen that Palm and Von Mold observed about the same 

 time the singular phenomenon of the spontaneous revolving movement of 

 t wining-plants. Palm (S. 58), I presume, observed likewise the revolving move- 

 ment of tendrils ; but I do not feel sure of this, for he says very little on the 

 subject. Dutrochet fully described this movement of the tendril in the com- 

 mon Pea. Mold first discovered that tendrils were sensitive to contact; but 

 from some cause, probably from observing too old tendrils, he was not aware 

 how sensitive they were, and thought that prolonged pressure was necessary to 

 excite movement . Professor Asa Gray, in a paper already quoted, first not iced 

 theextreme sensitiveness and rapidity of movements in the tendrils of certain 

 Cucurbit aceous plants. 



t This and the following drawings, from which the woodcuts have been en- 

 graved, were carefully made I'm- me from living plants by my sen Mr. George 

 If. Darwin. 



