96 



THE RATE OF GROWTH 



[CH. 



The several values in this table he very nearly (as we see by 

 Fig. 20) in a smooth curve; in other words a definite law, or 

 principle of continuity, connects the rates of growth at successive 

 points along the growing axis of the root. Moreover this curve, 

 in its general features, is singularly hke those acceleration-curves 

 which we have already studied, in which we plotted the rate of 

 growth against successive intervals of time, as here we have 

 plotted it against successive spatial intervals of an actual growing 



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Zones 



Fig. 20. Rate of growth in successive zones near the tip of the bean-root. 



structure. If we suppose for a moment that the velocities of 

 growth had been transverse to the axis, instead of, as in this case, 

 longitudinal and parallel with it, it is obvious that these same 

 velocities would have given us a leaf-shaped structure, of which 

 our curve in Fig. 20 (if drawn to a suitable scale) would represent 

 the actual outhne on either side of the median axis; or, again, 

 if growth had been not confined to one plane but symmetrical 

 about the axis, we should have had a sort of turnip-shaped root, 



