spiral turns round a thin stick, if free from twigs; it then ran
straight up for a space, and reversing its course took one or two
turns in an opposite direction. This reversal of the spire occurred
in all the foregoing species. The leaves are so small compared with
those of most of the other species, that the petioles at first seem
ill-adapted for clasping. Nevertheless, the main service of the
revolving movement is to bring them into contact with surrounding
objects, which are slowly but securely seized. The young petioles,
which alone are sensitive, have their ends bowed a little downwards,
so as to be in a slight degree hooked; ultimately the whole leaf, if
it catches nothing, becomes level. I gently rubbed with a thin twig
the lower surfaces of two young petioles; and in 2 hrs. 30 m. they
were slightly curved downwards; in 5 hrs., after being rubbed, the
end of one was bent completely back, parallel to the basal portion;
in 4 hrs. subsequently it became nearly straight again. To show how
sensitive the young petioles are, I may mention that I just touched
the under sides of two with a little water-colour, which when dry
formed an excessively thin and minute crust; but this sufficed in 24
hrs. to cause both to bend downwards. Whilst the plant is young,
each leaf consists of three divided leaflets, which barely have
distinct petioles, and these are not sensitive; but when the plant is
well grown, the petioles of the two lateral and terminal leaflets are
of considerable length, and become sensitive so as to be capable of
clasping an object in any direction.

When a petiole has clasped a twig, it undergoes some remarkable
changes, which may be observed with the other species, but in a less
strongly marked manner, and will here be described once for all. The
clasped petiole in the course of two or three days swells greatly,
and ultimately becomes nearly twice as thick as the opposite one