66 MB. DABWIN ON CLIMBING PLANTS. 



tendril itself bends and revolves in harmony with the internode, 

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

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

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

 direction followed is variable, either w;ith 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 lh. 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 lino 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 Dutrochet 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 in 



