198 
rubbing might be a maximal one. The following experiments, 
however, in which contact with varying degrees of pressure is 
applied, after the epidermis has been removed from the concave 
surface of the hook, in some case the injury extending down 
to, and causing the death of, the cambium over the region 
injured, so that contact takes place with formed wood tissue 
only, shew, that in such cases, if the strain set up in the hook 
by contact is sufficiently strong, a marked response is still 
produced, 
Uncaria sclerophylla. Single unpaired hooks are marked. * 
Injury extending to cambium on 
concave surface. S—S A—P S—S A—P 
Strong strain and pressure, touching After 4 weeks. 610 . 630 [155 . 390] 
inj only. 
injured part 
Portion only of epidermis removed from 217.515 [162 . 392]* 
187.447 [173 . 387] 
Slight injury to outer cortical layers. After 6 weeks. 232.505 [190.375] 
Apical shoots etc. removed. After 15 days. 
Epidermis removed 1) but ini D° but with contact 
from concave sur- d s snare and strong pressure 
. face and injured aE pe cama. touching injured 
part in contact. 0 contact. part only. 
Epidermis removed 
from concave sur- 
face. No contact. 
tl 
S—S A—P S—S A—P | s—_s a—P S—3 A—p | S~—S A—P S—S A—P | S—S A—P S—S A-P 
385 . 650 [250 . 540]* | 370. 620 [195 . 420] | 357. 705 [235 . 545]* | 435 . 550 [170 . 385] 
isan AON 
285 . 545 [180.390] | 292. 560 (487. 582}}| + Average of normal hooks in contact 
with 
ith strong pressure. 
The numbers in brackets, with the exception of that marked 
t, are the averages of similar but untouched hooks. The basal 
3 mm., at the distal point of which the measurements ar 
taken, is left uninjured in all cases. 
An injury to the hook, such as is caused by removing the 
epidermis over a small area, acts, especially if on the concave 
surface, as a distinct, though not very strong, stimulus to growth, 
and this mainly in the plane of the injury, i.e. if injured 0? 
