200 
in thickness, a corresponding unattached: hook measuring after 
the same time: O45 290. The breaking strain for the above 
attached hook was 8 kilo’s. 
Without contact, there is no marked difference bet Wed the 
growth on the concave and convex surfaces, but at the sides, the 
wood cylinder finally becomes somewhat thicker, than it does 
elsewhere. The hook responds most rapidly to contact, when — 
the normal curvature is just, or nearly, complete, and the hook 
is almost fully grown. In such hooks, when in contact, an effect 
is perceptible on the 32 day, and distinct on the 5**, even when 
the pressure and strain are relatively weak. 
1st day. 3rd day. 5th day. 
SS A—P S—S A—P S—S A—P S—S A-P s—-S A—P 8s-S A-P 
120 . 185 [120 . 130] 125.155 [120 . 140] 130 . 190 [125 . 145] 
The maximum irritability is attained between the 2" and 
4th week, but the power of responding to contact remains till 
after the 6t* week, when the epidermal layers begin to become 
corky and the hook quite hard and woody. 
If a loop of twine be tied fairly tightly on a young hook, 
an abrupt bend of from 20° to 40° may be produced at the 
point of contact. This is probably due to a direct mechanical 
effect upon the growing tissues, for with a loose loop of twine, 
it is not produced. A loosely tied loop of twine attached to 
the hooks produces a distinct result, and that almost entirely 
by rubbing and contact, for,a weight of as little as 0.3 grm. 
is hardly sufficient to set up any marked strain in the hook. 
Each of the numbers given below is, as usual, the average of 
6 experiments, and the i eiients are taken at a point 
2 mm. distant from the base. 
After 18 days. After 3. weeks. 5 weeks. 0.3 grm. | 6 weeks. 0.2 grm. 
0.4 grm. 0.3 grm. 
s—S A—P Untoue 
Si Similar but 
S—S A—P untouched. | S—S A—P untouched. —P Untouched. 
163. 209 [127 . 169] | 115. 160 (100. 139] | 157. 933 [150 "198) | 195 . 205 (100. 145) | 
oa dl a SA sre = 
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