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BULLETIN OF THE BUREAU OF FISHERIES 
so irregular as to make it impossible to use this curve, but the clam data are suffi- 
ciently uniform to give fairly smooth acceleration curves, as seen in Figure 4 A. 
Since one can not readily see from the velocity curve the relative changes with 
time — the gain per unit of size — it becomes necessary to plot the ratio diagram of 
growth as in Figure 5. Minot (1908) emphasized the importance of relative growth. 
He says: “It is evident that the increase in weight depends upon two factors — first, 
AGE IN YEARS 
Figure 5.— Ratio diagram of the growth of Cardium corbis at Snug Harbor 
upon the amount of body substance, or, in other words, of growing material present 
at a given time; second, upon the rapidity with which that amount increases itself.” 
The “intensity” of growth can be shown only by the relative method. To do this the 
logarithms of the lengths have been plotted on the age. As a result, equal vertical 
distances represent equal relative changes, and equal slopes mean equal relative rates. 
of relative growth (log Pl) of Cardium corbis at Snug Harbor 
Early growth is emphasized and late growth is minimized as a natural result of the 
relative aspect. 
The differentials of the logarithmic lengths may be derived and plotted just as 
in the case of the absolute lengths. The first differential, in Figure 6, shows the 
declining relative growth rate so much emphasized by Minot. The decline of relative 
growth is an orderly process and may be fitted mathematically to some function of 
