422 
PHYSIOLOGY 
Similarly the increase in forty hours of twelve 3.5 mm. spaces of a stem of 
Phaseolus: 
1 II III IV V VI VII VIII IX X XI XII 
2 2.5 4.5 6.5 5.5 3.0 1.8 i.o i.o 0.5 0.5 0.5 
Inspection of these records shows that the two younger millimeters of the root 
and the seven older are growing less rapidly than the third ; in the stem the four- 
teenth to the seventeenth millimeters (space IV) are growing most rapidly, and 
beyond this the older a division is the more slowly it grows. 
Growing regions. Comparison of the total length of root and stem 
still growing appreciably shows a striking difference. About i cm. 
Y 
7? 
70 
70 
60 
50 
40 
30 
7 
\ 
7 
\ 
20 
t 
MM 
DAYS-* 1 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 
FIG. 663. Grand curve of growth (solid line): the first day of the observation was 
evidently after fairly rapid growth had begun ; it attained a maximum on the fifth day, 
with an increment of 72 mm.; thence the rate falls off rapidly, and on the sixteenth day 
is only 18 mm.; growth rate magnified 10 times. The temperature curve (broken line) 
for the same days runs between 71 and 77 F. From data by SPOEHR. 
of the root and more than 4 cm. of the stem is shown to be growing 
by the record above. In general the total elongating portion of a root 
scarcely exceeds this; but in many stems 10-20 cm. are found elon- 
gating, and in twining plants 40-60 or even 80 cm. may be growing. 
