138 TENDRIL-BEARERS. Chap. IV. 



taneously from side to side ; and on a very hot day 

 one made two elliptical revolutions, at an average rate 

 of 2 hrs. 15 m. During these movements a coloured 

 line, painted along the convex surface, appeared after 

 a time on one side, then on the concave side, then on 

 the opposite side, and lastly again on the convex side. 

 The two branches of the same tendril have independent 

 movements. After a tendril has spontaneously revolved 

 for a time, it bends from the light towards the dark : 

 I do not state this on my own authority, but on that 

 of Mohl and Dutrochet. Mohl (p. 77) says that in a 

 vine planted against a wall the tendrils point towards 

 it, and in a vineyard generally more or less to the 

 north. 



The young internodes revolve spontaneously ; but 

 the movement is unusually slight. A shoot faced a 

 window, and I traced its course on the glass during 

 two perfectly calm and hot days. On one of these 

 days it described, in the course of ten hours, a spire, 

 representing two and a half ellipses. I also placed 

 a bell-glass over a young Muscat grape in the hot- 

 house, and it made each day three or four very small 

 oval revolutions ; the shoot moving less than half an 

 inch from side to side. Had it not made at least three 

 revolutions whilst the sky was uniformly overcast, I 

 should have attributed this slight degree of movement 

 to the varying action of the light. The extremity of 

 the stem is more or less bent downwards, but it 

 never reverses its curvature, as so generally occurs 

 with twining plants. 



