66 MB. DABWIN ON CLIMBING PLANTS. 



tendril itself bends and revolves in harmony with the intemode^ 

 a considerably wider space than that here specified (and repre- 

 sented one-half reduced) is swept. Diitrochet observed an ellipse 

 completed in Ih. 20m.; I saw one completed in Ih. 30m. The 

 direction followed is variable, either Avith or against the sun. 



Dutrochet asserts that the petiole of the leaf spontaneously 

 moves, as well as the young internodes and tendrils ; but he 

 does not say that he secured the internodes; when this was done, 

 I never detected any movement in the petiole, except to and 

 from the light. 



The tendrils, on the other hand, when the internodes and pe- 

 tioles were secured, described irregular spires or regular ellipses, 

 exactly like those made by the internodes. A young tendril, only 

 1^ inch in length, revolved. Dutrochet has shown that when 

 a plant is placed in a room, so that the light enters laterally, the 

 internodes travel much quicker to the light than from it : on the 

 other hand, he asserts that the tendril itself moves from the light 

 towards the dark side of the room. "With due deference to this 

 great observer, I think he was mistaken, owing to his not having 

 secured the internodes. I took a young plant with highly sensi- 

 tive tendrils, and tied the petiole so that the tendril alone could 

 move; it completed a perfect ellipse in Ih. 30m. ; and I then turned 

 the plant half round, so that the opposite side faced the light, but 

 this made no change in the direction of the succeeding ellipse. 

 The next day I watched a plant similarly secured until the tendril 

 (which was highly sensitive) made an ellipse in a line exactly to 

 and from the light ; the movement was so great that the tendril 

 bent itself down at the two ends of its elliptical course into a line 

 a little beneath the horizon, thus travelling more than 180 degrees ; 

 but the curvature was fully as great towards the light as towards 

 the dark side of the room. I believe ]5utrochet was misled by not 

 having secured the internodes, and by having observed a plant of \ 

 which the internodes and tendrils, from inequality of age, no 

 longer curved or moved in harmony together. 



Dutrochet made no observations on the sensitiveness of the 

 tendrils ; these, whilst young and about an inch in length, with 

 the leaflets on the petiole only partially expanded, are highly 

 sensitive ; a single light touch with a twig on the inferior or con- 

 cave surface near the tip caused them quickly to bend, as did 

 occasionally a loop of thread weighing one-seventh of a grain. 

 The upper or convex surface is barely or not at all sensitive. 

 After bending: from a touch the tendril straightened itself ^ 



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