Have you never wondered, when you looked at a tangle of grape-vine or
morning-glory stems, how they came to twist themselves together so?
Perhaps you had some sort of a notion that they got tangled up as a
bunch of silk or a skein of worsted lying loose might do. Examine any
vine which you can find growing near you, and see how different the
tangle is from a snarl of thread, there is a regular twist, the branches
coiling in the same direction. In some plants the turn is from right to
left, in others from left to right.
There must, of course, be some reason for this, and we can best find it
out by taking a young plant, a seedling, and watching what it does from
the start.
It would be very natural to think that plants moved only as stones do,
because something pulled or pushed them; but this would not be a true
conclusion. Every plant that we know much about is firmly fastened by
its root in the ground; the movements of its leaves and flowers seem
only caused by the blowing of the wind or the beating of the rain. But
though plants are anchored fast to the earth, they are all the while
moving as they grow.
[Illustration: Fig. 1.--THE BEAN. FIRST LEAVES IN DIFFERENT STAGES.]
[Illustration: Fig. 2.--MOVEMENT OF ROOT OF BLACK BEAN.
A, Position at nine o'clock.