207 
buted over all 3 areas of the hook, whereas witb local stimu- 
lation, such as an injury, or localized contact, exert, the response, 
also, is almost entirely local, in some cases, the growth in the 
other parts of the hook falling below the normal. 
In the following experiments, the growth in thickness at “2” 
is taken, as representing that of the entire hook, which, when 
comparative measurements are made, it does very nearly exactly. 
The data given, are the averages of 6 to 10, or more, experi- 
ments; a, 6 and ¢ are taken after 3 weeks, the rest all after 
5 weeks. The numbers in brackets give the averages of similar 
untouched hooks. 
S—S A—P S—S A—P 
(2). Cu wire round backs of hooks, moderate pressure. 135 . 270; [100 . 220] 
(4). Rough bamboo peg, 3 grm. weight inserted, fitting tightly. 230.295; [204.259] 
(c). Glass-rod no” ” " " ” 216 . 276; [204 . 259] 
(d). Attached to branches 3'/, to 4!/, mm. diameter. 375.439; [159 . 283] 
(e). Epidermis removed along concave inner edge. 195.305; ww ow 
(f). Hooks clasping one another, fairly strong pull. 262.262; wv wm 
(g). Attached obliquely to support, strain oblique. 300. 360; [115 . 210] 
(h). Loosely attached to branches of 2 to 3 mm. diameter. 943.895; a” wm 
(i). Injured to cambium, wood exposed along concave edge of “2”. 272. 304; wv om 
tightly clasping fixed support. 367.388; #7 
J). NW Wd W ‘PP 
(4). Bound tightly round back with loops of Cu wire, injured to 
Woo 935 . 380; [150.280] 
(2). Bound tightly onal back with loops of twine, uninjured. 157.300; [135 . 275] 
(m). Concave surface of “2” injured to cambium, and 1 grm. loop 
wire attache 
of Cu 185.290; [127 . 240] 
(z). Uninjured and 1 grm. loop of Cu wire attached. 155 . 265; 
W " 
Removal of the epidermis, along the concave surface, causes 
a specially marked increase in the antero-posterior diameter, 
but, if the injury extends to the cambium, the increase is mainly 
in the lateral diameter, for the reason that, in the other plane, 
growth can take, place in one direction only, namely on the ——- 
side. In a firmly attached hook, subject to strong strain, the 
increase in thickness is less, when previously injured, than cain 
uninjured; but if the stimulus is only slight, the uninjured 
hook grows more, than a similar but uninjured one. In the first 
case, the stimulus and injury act antagonistically, in the second, 
they summate. Hooks, interlocked with one another, respond by 
perfectly normal growth, commensurate to the strain, and the 
nature and area of the surfaces in contact. 
