1866. | | ( 257 ) 
III. BOTANY AND VEGETABLE PHYSIOLOGY. 
Enoianp.—Mr. Darwin, in an interesting paper “On the Phe- 
nomena of Motion and Sensitiveness in Climbing Plants,” hag 
shown that the unsupported, outstretched extremity of a hop or 
conyolvulus continues to revolve in circles, ever widening as it 
erows, and has calculated the rate of revolution, which varies in 
different plants, increases or decreases with a rise or fall of tempe- 
rature, is diminished by any disturbance such as jarring or moving 
the plant from place to place, and varies also with the age and the 
general health of the plant. Mr. D. also experimented on the sen- 
sitiveness of the petioles and internodes of such plants as the 
clematis, &c., which climb by their leaf-stalks. Some of the experi- 
ments were very delicate. “A loop of thread,” says Mr. D., “ weighing 
a quarter of a grain, caused the petiole to bend; a loop weighing 
4th of a grain sometimes acted, and sometimes not. In one instance, 
the weight of even the 2.th of a graim, brought into continuous 
contact with the petiole, caused it to bend through nearly 90°.” 
“ Young internodes alone are sensible on all sides along their whole 
length.” An internode, “rubbed six or seven times with a twig, 
became just perceptibly curved in one hour and fifteen minutes, 
and subsequently, in three hours, the curvature increased much; 
the imternode became straight again in the course of the night.” 
In numerous cases, particularly in Solanum Jasminoides, the 
clasping petioles increase in rigidity and thickness, the fibro-vas- 
cular bundles undergoing a change in their arrangement, so that 
from being originally semi-lunar on the cross-section, they develop 
into a close rmg lke that of an exogenous stem. Mr. Darwin 
thinks that both “leaf-climbers and tendril-bearers were primor- 
dially twiners ; that is, are the descendants of plants having this 
power and habit.” He regards plants which climb by tendrils ag 
the highest type of climbing plants. 
The following interesting and curious results were obtained 
from experiments on tendril-bearers. “A loop of soft thread, 
weighing .a.nd of a grain, placed most gently on the tip” of a tendril 
(Passiflora gracilis), “thrice plainly caused it to curve, as twice 
did a bent bit of platinum-wire, weighing ath of a grain; but this 
latter weight did not suffice to cause permanent curvature.” After 
being touched with a twig, the tip of a tendril begins to bend in 
from 25 to 29 seconds. ‘Transient irritation causes a tendril to 
coil imto an open helix, but it soon straightens itself again, 
recovering its sensibility. If, however, left in permanent contact 
with the irritating object, the spiral coil continues. It is a 
remarkable fact that no curvature of the tendril results from the 
touch of other tendrils, or the impact of drops of rain, to which 
