12 MR. DARWIN ON CLIMBING PLA2JTS. 



dozen had its leaves arranged in a perpendicular line: so I con- 

 clude that there is nothing remarkable in Palm's statement. 



The leaves of twining-plants rise from the stem (before it lias 

 twined) either alternately, or oppositely, or in a spire; in this 

 latter ease the line of insertion of the leaves and the course of 

 revolution or of twining coincide. This fact has been well shown 

 by Dutrochet *, who found different individuals of Solanum Dul- 

 camara twining in opposite directions, and these had their leaves 

 spirally arranged in opposite directions. A dense whorl of man y 

 leaves would apparently be incommodious for a twining plant, 

 and some authors have supposed that none have their leaves 

 thus arranged; but a twining Siphomeris lias whorls of three. 



If a stick which has arrested a revolving shoot, but has not as 

 yet been wound round, be suddenly taken away, the shoot gene- 

 rally springs forward, showing that it has continued to press 

 against the stick. If the stick, shortly after having been wound 

 round, be withdrawn, the shoot retains for a time its spiral form, 

 then straightens itself, and again commences to revolve. The 

 long, much-inclined shoot of the Ccropcgia previouslv alluded to 

 offered some curious peculiarities. The lower and older inter- 

 nodes, which continued to revolve, had become so stiff that they 

 were incapable, on repeated trials, of twining round a thin stick, 

 showing that the power of movement was retained after flexi- 

 bility had been lost. I then moved the stick to a greater dis- 

 tance, so that it was struck by a point 1h inches from the extre- 

 mity of the penultimate internode; and it was then neatly wound 

 round by this part and by the ultimate internode. After leaving 

 the spirally wouud shoot for eleven hours, I quietly withdrew the 

 stick, and in the course of the day the curled part straightened 

 itself and recommenced revolving ; but the lower and not curled 

 portion of the penultimate internode did not move, a sort of 

 hinge separating the moving and the motionless part of the same 

 internode. After a few days, however, I found that the lower 

 part of this internode had likewise recovered its revolving power. 

 These several facts show that, in the arrested portion of a re- 

 volving shoot, the power of movement is not immediately lost, 

 and that when temporarily lost it can be recovered. When a 

 shoot has remained for a considerable time wound round its 

 support, it permanently retains its spiral form even When the 

 support is removed. 



* Comptcs Eciidus, 1844, torn. xix. p. 295, and Annales des Soc. Nat. 

 3rd scries, Bot., torn. ii. p. 1G3. 



