branches. A forked twig placed so as to press lightly on the under
side of a young footstalk caused it, in 12 hrs., to bend greatly, and
ultimately to such an extent that the leaf passed to the opposite
side of the stem; the forked stick having been removed, the leaf
slowly recovered its former position.

The young leaves spontaneously and gradually change their position:
when first developed the petioles are upturned and parallel to the
stem; they then slowly bend downwards, remaining for a short time at
right angles to the stem, and then become so much arched downwards
that the blade of the leaf points to the ground with its tip curled
inwards, so that the whole petiole and leaf together form a hook.
They are thus enabled to catch hold of any twig with which they may
be brought into contact by the revolving movement of the internodes.
If this does not happen, they retain their hooked shape for a
considerable time, and then bending upwards reassume their original
upturned position, which is preserved ever afterwards. The petioles
which have clasped any object soon become much thickened and
strengthened, as may be seen in the drawing.

Clematis montana.--The long, thin petioles of the leaves, whilst
young, are sensitive, and when lightly rubbed bend to the rubbed
side, subsequently becoming straight. They are far more sensitive
than the petioles of C. glandulosa; for a loop of thread weighing a
quarter of a grain (16.2 mg.) caused them to bend; a loop weighing
only one-eighth of a grain (8.1 mg.) sometimes acted and sometimes
did not act. The sensitiveness extends from the blade of the leaf to
the stem. I may here state that I ascertained in all cases the
weights of the string and thread used by carefully weighing 50 inches
in a chemical balance, and then cutting off measured lengths. The