Chap. L TWINING PLANTS. 3 



may be seen to bend to one side and to travel slowly 

 round towards all points of the compass, moving, like 

 the hands of a watch, with the sun. The movement 

 very soon acquires its full ordinary velocity. From 

 seven observations made during August on shoots pro- 

 ceeding from a plant which had been cut down, and on 

 another plant during April, the average rate during hot 

 weather and during the day is 2 hrs. 8 m. for each revo- 

 lution ; and none of the revolutions varied much from 

 this rate. The revolving movement continues as long 

 as the plant continues to grow ; but each separate 

 internode, as it becomes old, ceases to move. 



To ascertain more precisely what amount of move- 

 ment each internode underwent, I kept a potted plant, 

 during the night and day, in a well-warmed room to 

 which I was confined by illness. A long shoot pro- 

 jected beyond the upper end of the supporting stick, 

 and was steadily revolving. I then took a longer stick 

 and tied up the shoot, so that only a very young inter- 

 node, If of an inch in length, was left free. This was so 

 nearly upright that its revolution could not be easily 

 observed ; but it certainly moved, and the side of the 

 internode which was at one time convex became concave, 

 which, as we shall hereafter see, is a sure sign of the 

 revolving movement. I will assume that it made at 

 least one revolution during the first twenty-four hours. 

 Early the next morning its position was marked, and it 

 made a second revolution in 9 hrs. ; during the latter 

 part of this revolution it moved much quicker, and the 

 tliird circle was performed in the evening in a little over 



