Cuap. II, LEAF-CLIMBERS, 81 
chief use of the coiling, at least whilst the plant is 
young, is to support the pitcher with its load of 
secreted fluid. 
Summary on Leaf-climbers——Plants belonging to 
eight families are known to have clasping petioles, and 
plants belonging to four families climb by the tips of 
their leaves. In all the species observed by. me, 
with one exception, the young internodes revolve more 
or less regularly, in some cases as regularly as those 
of a twining plant. They revolve at various rates, - 
in most cases rather rapidly. Some few can ascend 
by spirally twining round a support. Differently from 
most twiners, there is a strong tendency in the same 
shoot to revolve first in one and then in an opposite 
direction. The object gained by the revolving move- 
ment is to bring the petioles or the tips of the leaves 
into contact with surrounding objects; and without this 
aid the plant would be much less successful in climb- 
ing. With rare exceptions, the petioles are sensitive 
only whilst young. They are sensitive on all sides, 
but in different degrees in different plants; and in 
some species of Clematis the several parts of the same 
petiole differ much in sensitiveness. The hooked 
tips of the leaves of the Glortosa are sensitive only on 
their inner or inferior surfaces. The petioles are sen- 
sitive to a touch and to excessively slight continued 
pressure, even from a loop of soft thread weighing 
only the one-sixteenth of a grain (4:05 mg.); and 
there is reason to believe that the rather thick and 
