201 
Where the loop is in contact with the hook, a slight but 
distinct localized swelling can generally be seen. oe one a 
hook measured at the sauna. point of contact: 170 : 315, 
A—P 
2mm. opis - pte being: 130 130, and 2 mm. nearer the 
base being, 145. 195. The breaking strain for this hook was 
s—S A—P 
1 kilo, whereas a similar but untouched hook (115. 165) broke 
with '/, kilo. A slight contact stimulus such as the above, there- 
fore, though partly localized, nevertheless is also transmitted 
to, and influences the growth of all parts of the hook. 
The hook is sensitive to a strong strain, wherever the con- 
tact may be applied. Thus, if bound round the back with Cu 
S—S A—P 
wire, the hooks averaged after 6 weeks: 175 . 215; with loose 
loops of Cu wire weighing 0.2 grm. attached, they averaged 
S—S acl 
a0 200, if slit to the cambium for a few m.m. on concave 
s—S A—P 
surface, they averaged, 140.195, whilst normal untouched hooks 
s—S A—P 
averaged after 6 weeks: 100 . 145. 
As in Uncaria, an injury acts as a stimulus to growth. Thus 
8 hooks, from which a small, piece of epidermis was removed 
on the concave surface, averaged after 4 weeks (the injury 
a Sb above the point, at which the measurements are taken): 
Ml . 159, whereas 8 similar, but untouched hooks , averaged : 
107 ? 136. The difference is slight, but so also is the stimulus, 
and the increase of growth is almost entirely on the concave 
surface, which is the one stimulated. 
A smooth surface acts as a less powerful stimulus, than a 
rough one. Thus 10 hooks, in which were inserted wooden 
pegs 0.5 em. camer and weighing 1.2 grammes, averaged after 
1% days: 169. oF 39: whereas similar ones, holding loose gine — - 
the same diameter but weighing 2.4 grammes, averaged: Ro 56 234, 
and similar, but untouched hooks, averaged 126 | | 164; after 
25 days the numbers being: 250 . 282, 201 . 258, 142 . 176, 
tespectively. Hence, in the above experiment, a rough ommne 
Ann. Jard. Buitenz. Vol. XV, 1. 
