which has clasped nothing. When thin transverse slices of the two
are placed under the microscope their difference is conspicuous: the
side of the petiole which has been in contact with the support, is
formed of a layer of colourless cells with their longer axes directed
from the centre, and these are very much larger than the
corresponding cells in the opposite or unchanged petiole; the central
cells, also, are in some degree enlarged, and the whole is much
indurated. The exterior surface generally becomes bright red. But a
far greater change takes place in the nature of the tissues than that
which is visible: the petiole of the unclasped leaf is flexible and
can be snapped easily, whereas the clasped one acquires an
extraordinary degree of toughness and rigidity, so that considerable
force is required to pull it into pieces. With this change, great
durability is probably acquired; at least this is the case with the
clasped petioles of Clematis vitalba. The meaning of these changes
is obvious, namely, that the petioles may firmly and durably support
the stem.

Clematis microphylla, var. leptophylla.--The long and thin internodes
of this Australian species revolve sometimes in one direction and
sometimes in an opposite one, describing long, narrow, irregular
ellipses or large circles. Four revolutions were completed within
five minutes of the same average rate of 1 hr. 51 m.; so that this
species moves more quickly than the others of the genus. The shoots,
when placed near a vertical stick, either twine round it, or clasp it
with the basal portions of their petioles. The leaves whilst young
are nearly of the same shape as those of C. viticella, and act in the
same manner like a hook, as will be described under that species.
But the leaflets are more divided, and each segment whilst young
terminates in a hardish point, which is much curved downwards and