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THE AMERICAN NATURALIST [Vol.L 



lation anew. With the idea that these tables may possibly be 

 useful to others, they are given herewith. In making use of such 

 tables it is necessary only to reduce to the basis of a common total 

 the observed F 2 zygotic series and any series of the table with 

 which a comparison is desired. The total given in the table is in 

 each case the lowest one which involves no fractions. If one uses 

 the tables, such formulae as Emerson's (II-IV) will not be found 

 necessary in estimating the strength of the linkage. Moreover 

 those formulae are less useful than tables in dealing with the modi- 

 fied dihybrid ratio, 9:3:4, which happens to have been the first 

 case that I encountered in my own work. The modified ratio as 

 affected by linkage may be read directly from the table by com- 

 bining classes aB and ab. 



TABLE II 



July 10, 1916 



W. E. Castle 



