568 



THE AMERICAN NATURALIST [Vol. XL V 



to obtain the products of the frequencies of all of the columns by 

 all the strips, but by doing so a check is obtained for all entries 

 except those of the diagonal cell. 



The great advantage of this method is that it replaces mental 

 and pencil drudgery with rapid mechanical calculation. Clip- 

 ping the movable column by the side of the one with which it 

 is to be compared in the table, one can obtain the products and 

 the sum of the products simultaneously on a Brunsviga, 6 by 

 merely multiplying the successive pairs of frequencies together 

 and allowing the products to accumulate. Of course the fre- 

 quencies for the diagonal cell can be quickly obtained, by sum- 

 ming the n{n — 1) values for the individual column, in pre- 

 cisely the same manner. 



Purely as an illustration of method the intra-individual or 

 homotypic correlation for number of seeds developing per pod 

 in a series of Broom plants {Cytisus scoparius) 1 collected at 

 Woods Hole in the late summer of 1907 will now be determined. 

 TABLE I 



7 The variability of these has already been compared with that of Pear- 

 the Broom, Cytisus scoparius," Amer. Nat., Vol. 43, pp. 350-355, 1909. 



