Pe st. ee eee ae aie 
231 
the free portion of the secondary leaf assumes its normal 
position. Not only the terminal but also the pulvini of the 
other secondary leaves, will twine around a support, but being 
shorter, they can only form a complete coil when the support 
is less than 0.5 cm. in diameter, and the thickening induced 
by contact is much less marked. 
It depends entirely on which side is in contact, as to which 
finally becomes and remains concave. As a general rule it is 
the proximal side of the distal pair of pulvini which becomes 
permanently concave, owing to the pressure being generally 
applied to this surface, when accidental contact takes place, 
but under appropriate condition of contact any side may be- 
come the concave one. 
Rubbing with a glass rod produces a curvature, but not so 
rapidly or markedly as rubbing with a wooden one does. Mere 
contact, however prolonged, with a glass rod, may cause a slight 
curvature but never complete coiling, the latter only taking 
place when moderate pressure exists between the glass rod 
and the surface of the pulvinus with which it is in contact. 
Contact between a pair of tendrils of the same or another branch 
is sufficient, especially if moderate pressure exists between the 
surfaces in contact, to cause them to coil, harden and thicken. 
Pulvini in “self” contact averaged. After 2 weeks, 238.100ths of a mm. diam. at base, 
without contact 200.100ths of a mm. 
Apical pair in contact with loose twig 0.5 cm. diam. and 1 grm. weight. After 2 weeks, 
275.100ths of a mm. diam. at base, without contact 220.100ths of a mm 
2nd pair in contact with loose twig 0.5 em. diam. and 1 grm. weight. After 2 weeks, 
: i .100ths of a mm. 
ae astern ona phageeidanirer ser in 16 days averaged. After 
2 weeks, 309.100ths of a mm. diam. at base, without contact 193.]00ths of a mm. 
A bamboo fibre | mm. diameter and weighing 0.1 grm. is 
sufficient to cause a curvature and just perceptible thickening, 
but it is only when the pulvinus is attached to a fixed support 
and subjected to a marked strain, that the full possible increase 
in thickness takes place. In inducing curvature and coiling, it 
is the nature of the surface in contact which is chiefly im- 
portant, but the amount of thickening is mostly dependent 
upon, and is produced almost entirely in direct: response to, 
