INTRODUCTION.

THE chief object of the present work is to describe and connect together
several large classes of movement, common to almost all plants. The most
widely prevalent movement is essentially of the same nature as that of the
stem of a climbing plant, which bends successively to all points of the
compass, so that the tip revolves. This movement has been called by Sachs
"revolving nutation;" but we have found it much more convenient to use the
terms circumnutation and circumnutate. As we shall have to say much about
this movement, it will be useful here briefly to describe its nature. If we
observe a circumnutating stem, which happens at the time to be bent, we
will say towards the north, it will be found gradually to bend more and
more easterly, until it faces the east; and so onwards to the south, then
to the west, and back again to the north. If the movement had been quite
regular, the apex would have described a circle, or rather, as the stem is
always growing upwards, a circular spiral. But it generally describes
irregular elliptical or oval figures; for the apex, after pointing in any
one direction, commonly moves back to the opposite side, not, however,
returning along the same line. Afterwards other irregular ellipses or ovals
are successively described, with their longer
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axes directed to different points of the compass. Whilst describing such
figures, the apex often travels in a zigzag line, or makes small
subordinate loops or triangles. In the case of leaves the ellipses are
generally narrow.

Until recently the cause of all such bending movements was believed to be
due to the increased growth of the side which becomes for a time convex;
that this side does temporarily grow more quickly than the concave side has
been well established; but De Vries has lately shown that such increased