154 TENDRIL-BEARERS. Cuar. IV. 
1 hr. 1m. Theapex of the tendril describes elongated 
ellipses, sometimes narrow and sometimes broad, with 
their longer axes inclined in slightly different direc- 
tions. The plant can ascend a thin upright stick by 
the aid of its tendrils; but the stem is too stiff for it 
to twine spirally round it, even when not interfered 
with by the tendrils, these having been successively 
pinched off at an early age. 
When the stem is secured, the tendrils are seen to 
revolve in nearly the same manner and at the same 
rate as the internodes.* The tendrils are very thin, 
delicate, and straight, with the exception of the tips, 
which are a little curved; they are from 7 to 9 inches 
in length. <A half-grown tendril is not sensitive ; ‘but 
when nearly full-grown they are extremely sensitive. 
A single delicate touch on the concave surface of the 
tip soon caused one to curve; and in 2 minutes it 
formed an open helix. A loop of soft thread weighing 
aynd of a grain (2:02 mg.) placed most gently on the 
tip, thrice caused distinct curvature. A bent bit of 
thin platina wire weighing only =yth of a grain (1:23 
mg.) twice produced the same effect; but this latter 
weight, when left suspended, did not suffice to cause a 
permanent curvature. These trials were made under . 
a bell-glass, so that the loops of thread and wire were 
* Prof. Asa Gray informs me temperature varying from 88°-92¢ 
that the tendrils of P. acerifolia ahr.) in the following times, 
revolve even at a quicker rate 40 m.,45m., 383 m., and 46 m. 
-than those of P. gracilis; four One half-revolution was per- 
revolutions were completed (the formed in 15 m. 
