Cuap. I. 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, 12 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 
revolying 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 
third circle was performed in the evening in a little over 
