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THE AMERICAN NATURALIST [Vol. XLIX 



In dealing with egg production Pearl and Surface 2 give as the 

 correlation in number of eggs for first and second year 



r = . 032 ±.083, 



a value which, though positive, is clearly insignificant with re- 

 gard to its probable error. 



Thus in this particular case the performance of the first year 

 furnishes no clue to that of the second. With respect to egg- 

 laying capacity, the record of the pullet year furnishes no cri- 

 terion for elimination from the flock. 



For milk yield in cattle the case seems to be quite different. 

 Gavin 3 has found that there is a medium correlation between (a) 

 the ' ' revised maximum ' ' 4 yield in quarts of successive lactations, 

 and (&) between the "revised maximum" of the individual 

 lactation periods and the highest revised maximum reached by 

 the animal. 



So far as I am aware the only worker who has published 

 correlations between the characters of the same plant individuals 

 in different years is Clark 3 whose results have been noted in these 

 pages by Pearl. 



The correlation tables and constants show that plants of a 

 given class in any year (height or weight of hay produced) will 

 be highly variable in a subsequent year, but will on the average 

 deviate from the mean of the whole culture of the year in the 

 same direction and to about half the extent of the type selected 

 in the preceding year. Thus if selection were made on the basis 

 of a single year's test only, many individual plants of low yield 

 would be discarded which in a subsequent year would have taken 

 higher rank, while high-yielding plants would be retained which 

 subsequently would give disappointing results. On the whole, 

 however, the yield of a hay plant one year does furnish a valu- 

 able index to its yield in a subsequent year. 



2 Pearl, E. and F. M. Surface, "A Biometrical Study of Egg Produc- 

 tion in the Domestic Fowl," I, Bull. Bu. Anim. Ind., 110, 66, 1909. 



3 Gavin, Wm., "Studies in Milk Eecords: On the Accuracy of Estimat- 

 ing a Cow 's Milking Capacity by Her First Lactation Period. ' ' Jour. Agr. 

 Sri., 5, 377-390, 1913. 



* "Revised Maximum" milk yield is the maximum day yield which is 

 three times reached or exceeded in a lactation. 



s Clark, C. F., "Variation and Correlation in Timothy," Bull. Cornell Agr. 

 Exp. Sta., 279, 1910. 



e Pearl, R., Amer. Nat., 45, 418-419, 1911. 



