214 
A hook-tendril cannot form a complete coil around a stem 
of more than 0.7 cm. diameter. If the stem, originally thinner 
than this, has grown in thickness, since the hook-tendril coiled 
around it, it may be compressed or even strangulated. The opti- 
mal thickness of a support, for coiling, and for growth in 
thickness, is 0.4cm., beyond this, an increase in the diameter 
of the support is not only inimical to perfect coiling, but also 
inhibits to a certain extent the growth in thickness resulting 
from the contact. 
In the young hook, the lateral and antero-posterior diameters 
are equal, but, when in contact, the latter increases more rapidly 
than the former. Finally however, when the hook is nearly 
fully grown, and the pressure on the concave surface in contact 
considerable, the latter becomes flattened, its growth ceases, and 
the lateral diameter comes to exceed the antero-posterior one. 
The breaking strain for the hooks 1*, averaged 9 to 10 kilo’s 
for 2*, 5 to 6 kilo’s, the break as usual taking place at the 
top of the first bend. The stalks of 1* averaged 2 mm. in 
diameter (unattached °/,, to 1 mm.), and broke with from 11 
to 12 kilo’s. Hence, in the adult attached hook, the breaking 
strain for the different parts of the hook is largely equalized; 
whilst, in the young attached hook, the breaking strain for the 
peduncular portion is considerably greater, than for the coiled 
attached portion. 
A branch of Strychnos laurina, 1 cm. diameter at the base, and 
31/, metres long, weighed fresh, with the leaves, hooks, and lateral 
branches: 370 grammes, .*. one adult hook could at the utmost 
9000 13 
support 370 x {T= 79 metres, or allowing ; as the factor of 
safety, = 13 metres. It is interesting to notice, that, in all the 
hook climbers, a distinct relation exists between the strength 
of the fully developed hook and the weight of a given length 
of the stem, in all cases the lengths of stem, which a single 
hook can support, being remarkably similar. 
The hook tendrils are fully sensitive to contact with one 
another, and respond, in a normal manner, commensurate to 
