120 A MANUAL OF MENDELISM 



yield through the admixture of smaller yielding varieties 

 — that is through impurities — the society's work resolved 

 itself into : 



(a) Procuring good yielding varieties from other countries. 



(6) Finding the best yielding native varieties. 



(c) Growing these side by side and comparing their yields. 



{d) Eliminating the poor varieties and propagating the 

 good till a stock had been accumulated. 



(e) Keeping the good varieties pure and purifying the 

 impure. 



(/) Distributing the good varieties among members of 

 the association and other farmers. 



The association acquired land at Svalof and appointed 

 a director to carry on the work, in which, for ten or 

 twelve years, little else was accomplished beyond finding 

 and testing varieties and keeping the best ones up to 

 standard of purity. Attempts were made to improve 

 some varieties, but with little success. During this 

 period, influenced chiefly by the Darwinian theory of 

 evolution, it was believed that improvement was to 

 be accomplished by what has been called the method of 

 continuous mass selection. This method may be applied 

 to the grain or the plant or to both. It is usually applied 

 to the grain by means of the riddle which has the effect 

 of rejecting a proportion of the smaller seeds in accord- 

 ance with the size of the mesh and the vigour with 

 which the riddle is worked. Applied to the plant, it 

 consists in eliminating by hand such plants as are clearly 

 different from the bulk in size, length of straw, thickness 

 of straw, length of head, shape of head, and so on. 



It is obvious that this method increases the purity 

 of a variety so far as size of grain and certain plant 

 characters are concerned, but it does not necessarily 



