190 
are measured here before and after contact. The extreme base 
of the hook of Uxcaria becomes fairly large along the antero- 
posterior diameter, even in unattached hooks, and hence relatively 
less growth takes place in this direction at the extreme 
base, when attached. When comparing the effects of different 
stimuli with one another, the resultant growth may be more 
rapid in one case than in the other, but yet, cease at the same 
point in both cases; or it may proceed at the same rate but 
continue for a longer time and reach a higher level in one 
case, than in the other. Hence it is important to know both 
the amount of growth in a given time, and the total final growth. 
As a general rule, however, a stronger stimulus causes an in- 
crease in both the rapidity and the final amount of growth. The 
following experiment shews, that a difference between the rates 
of growth of attached and unattached hooks, i. e. a response to 
stimulation , becomes perceptible after the 2n4 day, and is quite 
distinct on the 5th day. 
Uncaria sclerophylla. (paired hooks) : 
Hooks attached to loose piece of stick. | Fixed support. Strong pull on hook. 
1st m e 
a After 2 days. | 5 days. 1s otergaig 2 days. 5 days. 
S—S} 160 [160] *) | 170 [165] | 200 [168] | 170 [150] | 200 [165] | 265 [170] 
—P| 430 [380] 435 [385] | 450 (390) 510 ta50} 520 +455] 540 [460] 
If a young actively growing shoot is selected, and from it, and 
the neighbouring branches and leaves, the apical buds and young 
leaves, are removed, the growth of the hooks is more rapid 
than normal and a still more rapid response to stimulation is 
shewn; in a single day, a difference between the rate of growth 
of stimulated and non stimulated hooks being perceptible *). Thus, 
1) The numbers in brackets are the averages of the opposite unattached hooks. 
For a growth change, the response is moderately rapid, though slow as compa 
for example, with the rapidity with which heterauxesis is induced in the perianth 
of Crocus by a change of temperature, 
2) Townsend (Ann. of Bot. 1897 p. 509) has shewn that an injury may cr 
an increased rapidity of growth extending several centimetres from the point of 
