218 
The hook-tendrils of Strychnos are intermediate between the 
hooks of Uncaria, Artabotrys etc. and tendrils. Between hook- 
tendrils , such as those of Strychnos, and the extremely sensitive 
highly specialized tendrils of Passifora, Sicyos etc. a variety of 
intermediate forms occur. Thus the tendrils of shrubby tropical 
climbers, as a general rule, when in contact, become more or 
less markedly thickened and stronger, and Darwin ') has shewn, 
that the same is the case in the petioles of leaf climbers, such 
as Solanum jasminoides, when attached. 
The change is not merely due to the lignification and scleren- 
chymatization of tissues already formed, as in Passifoora, 
Sicyos etc., but is accompanied by a more or less marked cam- 
bial activity, causing an increase in the thickness of the wood 
cylinder, just as is the case, to a more marked extent, in 
attached hooks or hook-tendrils. 
Amphilobium mutisii, H. B. and K. 
The tendrils of this plant form favourable experimental 
material for studying the causation of the increase of thickness, 
which they undergo, when attached. The trifid tendril has @ 
long common peduncular portion, the distal portion of which 
is distinctly though not markedly irritable, and may coil, when 
in contact, independently of the trifid apical portion, where the 
main irritability is localized. The three terminal tendril seg- 
ments are normally of equal length, and, without contact, finally 
become disarticulated from the peduncle, without attaining ® 
greater thickness than 60 to 75, 100ths mm., whilst the peduncle, at 
the same time loses the slight irritability, it originally posses: 
sed. If, however, one or more of the tendril segments become 
attached, all three generally persist, and the attached ea 
increase much more in thickness , and also, though to 4 less 
extent, in length, than the unattached. Thus: 
1) Darwin, Climbing plants. 1875. p. 179. 
