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 i cm. 



70 



60 



50 



40 



30 







20 



t 

 MM 



DA5B-* 1 2 3 4 5 6 7 8 9 10 II 12 13 M 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 fay 

 is only 18 mm.; growth rate magnified 10 times. The temperature curve (broken ane) 

 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. 



