134 TENDEIL-BEAKEGS. Chap. IV. 



with its extreme point, can work itself onwards until 

 it has passed twice or even thrice round the stick, 

 and has permanently grasped it. 



Hanhurya Mexieana. — The young intemodes and 

 tendrils of this anomalous member of the family, revolve 

 in the same manner and at about the same rate as those 

 of the Eehinocystis. The stem does not twine, but can 

 ascend an upright stick by the aid of its tendrils. 

 The concave tip of the tendril is very sensitive ; after 

 it had become rapidly coiled into a ring owing to 

 a single touch, it straightened itself in 50 m. The 

 tendril, when in full action, stands vertically up, with 

 the projecting extremity of the young stem thrown a 

 little on one side, so as to be out of the way ; but the 

 tendril bears on the inner side, near its base, a short 

 rigid branch, which projects out at right angles like 

 a spur, with the terminal half bowed a little down- 

 wards. Hence, as the main vertical branch revolves, 

 the spur, from its position and rigidity, cannot pass 

 over the extremity of the shoot, in the same curious 

 manner as do the three branches of the tendril of the 

 EeMnocystis, namely, by stiffening themselves at the 

 proper point. The spur is therefore pressed laterally 

 against the young stem in one part of the revolving 

 course, and thus the sweep of the lower part of the main 

 branch is much restricted. A nice case of co-adaptation 

 here comes into play : in all the other tendrils observed 

 by me, the several branches become sensitive at the 

 same period ; had this been the case with the Hanhurya, 

 the inwardly directed, spur-like branch, from being 



