of the ring of wood. This ring presented, both in a transverse and
longitudinal section, a closely similar structure to that of the
stem. It is a singular morphological fact that the petiole should
thus acquire a structure almost identically the same with that of the
axis; and it is a still more singular physiological fact that so
great a change should have been induced by the mere act of clasping a
support. {23}

FUMARIACEAE.--Fumaria officinalis.--It could not have been
anticipated that so lowly a plant as this Fumaria should have been a
climber. It climbs by the aid of the main and lateral petioles of
its compound leaves; and even the much-flattened terminal portion of
the petiole can seize a support. I have seen a substance as soft as
a withered blade of grass caught. Petioles which have clasped any
object ultimately become rather thicker and more cylindrical. On
lightly rubbing several petioles with a twig, they became perceptibly
curved in 1 hr. 15 m., and subsequently straightened themselves. A
stick gently placed in the angle between two sub-petioles excited
them to move, and was almost clasped in 9 hrs. A loop of thread,
weighing one-eighth of a grain, caused, after 12 hrs. and before 20
hrs, had elapsed, a considerable curvature; but it was never fairly
clasped by the petiole. The young internodes are in continual
movement, which is considerable in extent, but very irregular; a
zigzag line, or a spire crossing itself; or a figure of 8 being
formed. The course during 12 hrs., when traced on a bell-glass,
apparently represented about four ellipses. The leaves themselves
likewise move spontaneously, the main petioles curving themselves in
accordance with the movements of the internodes; so that when the
latter moved to one side, the petioles moved to the same side, then,
becoming straight, reversed their curvature. The petioles, however,