154 TENDRIL-BEARERS. Chap. IV. 



1 hr. 1 hi. The apex 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 

 g^nd 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 ^th 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 Fahr.) in the following times r 



revolve even at a quicker rate 40 m., 45 m., 38 m., and 46 m. 



than those of P. gracilis ; four One half-revolution was per- 



revolutions were completed (the formed in 1 5 m. 



