GROWTH UNDER CONSTANT EXTERNAL CONDITIONS. 
819 
5th day 17*0 mm. 
6th 14-5 
7th 7-0 
8th o-o 
In the same way I found that a piece at first 3-5 mm. long of the first inter- 
node of Phaseolus muliiflorus beneath the first pair of fohage-leaves, with a daily 
variation of temperature between 12*75° and 13*75° C, showed the folio whig in- 
crease : — 
ist day 
12 
2nd 
I '5 
3rd 
2*5 
4th 
5*5 
5th 
7-0 
6th 
90 
7 th 
140 
8th 
io*o 
9th 
7-0 
loth 
2*0 
Since every organ that is growing in length consists of zones of different ages, 
which are produced in succession from the primary meristem of the punctum vegeta- 
iionis (or of an intercalary vegetative zone), the successive zones of an internode 
or a root indicated by ink-marks must show different increments of growth in 
equal times. While the zone nearest the punctum vegetationts is beginning to grow, 
the next one has already entered on a later phase of its grand period, while one 
at a greater distance would have attained the maximum of its rapidity of growth, 
and a still further one would have ceased to grow. In other words, a number of 
zones below the cell-producing punctum vegetationis are in the ascending phase, 
while those lying further backwards are in the descending phase of their grand 
period ; or again, each zone is in a later phase of its period of growth the greater its 
distance from the punctum vegetationis. If the successive zones of a growing organ 
are indicated by the figures I, II, III, &c., and the increments of growth observed 
at the same time in each of them by I^, I2, I3, &c. ; then we have the following 
relationship : — 
I II III 1 IV V VI VII VIII 
I, < I2 < I3 < I, > I5 > Ig > I, > zero. 
There is therefore in the organ a region of maximum rapidity of growth. Thus, 
for example, I found in the first internode of Phaseolus multiflorus^ which was divided 
into twelve zones, each 3-5 mm. long, in the first forty hours : — 
Zone, Increment, 
(uppermost) . . ist 2*0 mm. 
2nd 2-5 
3rd 4*5 
4th e-5 
6th 5-5 
3 G 2 
