820 
MECHANICS OF GROWTH. 
iHL-l ClllCll I* 
6th 
3*0 mrn. 
7111 
i'8 
8th 
I'O 
9th 
I'O 
loth 
0-5 
nth 
(lowest) . 
. i2th 
05 
The maximum rapidity of growth lay therefore in the fourth zone, which was 
originally situated at a distance of about 10*5 mm. from the upper end of the inter- 
node. 
As it is usual for several contiguous internodes of stems to be growing at the 
same time, and the maximum rapidity of growth occurs, according to circumstances, 
in the second, third, fourth, or fifth internode beneath the bud, the region of most 
rapid growth is at a considerable distance from the apex of the stem, and especially 
when the internodes attain a considerable length and several are growing at the same 
time. In roots, on the other hand, the maximum rapidity of growth occurs much 
nearer the punctum vege/atmiis, usually at a distance of only a few millimetres ; 
and the portion of the root beneath its apex in which the chief part of the growth 
takes place is consequently only a few millimetres long, while in stems with long 
internodes it is often many centimetres in length. If therefore a root and a stem 
with long internodes are divided into zones of equal lengths, e.g. i mm., com- 
mencing from the punctum vegetatioms, the law of growth, as expressed by the 
general formula given above, is the same in both cases, but with this difference, 
that in the stem the number of zones that are increasing in length at the same time 
is much greater than in the root, in consequence of the fact that in the last case 
each zone completes its period of growth more quickly^; its curve is shorter and 
more abrupt. 
Thus, for example, in a primary root of Vicia Faha which grew in damp air 
and which was divided, starting from the punctum vegetatioms, into zones each i mm. 
in length; I found the following increments of growth in the first twenty-four hours 
at a temperature of 20*5° C. : — 
Zone. 
Increment. 
1 0th 
o*i mm. 
9 th 
0'2 
8th 
0-3 
7 th 
0-5 
6th 
13 
5th 
1-6 
4th 
35 
3rd 
8'2 
2nd 
5-8 
apex 
15 
^ It by no means however follows from this that the root grows more rapidly, i. e. attains in the 
same time a greater length than the stem. 
