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 1.0 1.0 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 1 cm. 



DAYS-* 1 



10 



»2 13 14 15 



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. 



