3o6 



Journal of Agricultural Research Voi. xvii. No. 6 



The histograms and their fitted curves are shown in figures i to 4. 



^ 15 

 A. 



5 10 



10 



7 9 11 13 15 17 19 21 23 25 27 29 



MEAN WEEKLY YIELD - GALLONS 



Fig. I. — Histograms and fitted curves for variation in mean weekly milk yield of Ayrshire cows of ages 

 3 to 7 years. The ordinates are plotted on a percentage basis, and since the base unit (i gallon) is the 

 same for all diagrams the areas of all are equal. 



