I tried this four times; the tendril generally rose to a horizontal
position in an hour or an hour and a half; but in one case, in which
a tendril depended at an angle of 45 degrees beneath the horizon, the
uprising took two hours; in half an hour afterwards it rose to 23
degrees above the horizon and then recommenced revolving. This
upward movement is independent of the action of light, for it
occurred twice in the dark, and on another occasion the light came in
on one side alone. The movement no doubt is guided by opposition to
the force of gravity, as in the case of the ascent of the plumules of
germinating seeds.
A tendril does not long retain its revolving power; and as soon as
this is lost, it bends downwards and contracts spirally. After the
revolving movement has ceased, the tip still retains for a short time
its sensitiveness to contact, but this can be of little or no use to
the plant.
Though the tendril is highly flexible, and though the extremity
travels, under favourable circumstances, at about the rate of an inch
in two minutes and a quarter, yet its sensitiveness to contact is so
great that it hardly ever fails to seize a thin stick placed in its
path.
Pages:
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174