221 
B. unguis a few points may be added. After the tendrils have 
grasped the bark of the tree up which the plant is climbing , 
a stronger and firmer attachment is formed by the roots, which 
arise from the neighbouring node, and though the tendrils may 
persist for a considerable time, the roots form the permanent 
attaching organs. Contact applied to the concave surface soon 
causes a distinct bending at the point of contact, the irritabi- 
lity and time of response being the same in the Tropics as 
Darwin found with a hot house plant in England. The removal 
of turgidity does not cause any perceptible straightening out of 
the curvature. 
In Nyctocalos Thomsonae a curvature begins to be perceptible 
in from 3 to 6 hours after contact has been applied, and is 
generally in 1 to 3 days completed, being then rarely more 
than a semicircle. The claw acts like a grappling iron, and 
the curvature causes the recurved, hard and sharp extremity 
to imbed itself more deeply and become more firmly fixed, when 
a strain is applied to the tendril. The claws even when quite 
young are not very flexible and, when older, are rather stiff 
and rigid, especially in the apical portion. If, as soon as a cur- 
vature is perceptible, the hooks are placed entire or in longi- 
tudinal vertical segments in 10 */ K NO, or (Correns’ method), 
first in absolute alcohol and then later in water, no straigh- 
tening takes place in the KN O,, and the curvature does not 
increase in the alcohol, or perceptibly diminish when returned 
to water. Hence if the curvature is originally produced by a 
difference in turgidity between the concave and convex sides , 
it is almost at once followed up by either growth or some 
counterbalancing change in the semi-elastic but compressible and 
distensible tissues of the two sides, placing them in equilibrium 
again and restoring isotonic turgidity. The fact, however, that 
in a thoroughly irritable «hook” the removal of not too pro- 
longed contact may be followed by @ straightening out of the 
curvature, points to the latter being directly caused by a change 
in turgidity, and along with the fact, that the hook undergoes 
no perceptible increase in thickness when in contact, marks 
