PURE LINES 9 



thing entirely new, or by the selection of a pure strain 

 from an old and valued stock. If an ordinary field 

 of barley is examined, a good many differences 

 between individual plants can be found ; some will be 

 taller, others longer in the ear, others blind of a few 

 corns on one side of the ear; variations, sometimes 

 of magnitude, exist in every part of the plant. Most 

 of these variations are due to accidents of nutrition 

 and disappear in the next generation. Thus a speci- 

 ally big grain generally yield but ordinary corn ; and 

 on the other hand small " tail " corn of a good stock, if 

 it gets through the early stages of growth, gives rise 

 to perfectly normal progeny. But some variations 

 are heritable and appear again without change in the 

 progeny when the grain from the special ears is sown 

 separately. It follows that the ordinary crop of a 

 given variety must be an aggregate of many different 

 strains, like every aggregate made up of some above the 

 average, and some below it. By breeding from single 

 ears the different strains can be isolated, and those 

 which yield best can be picked out and bred on to 

 constitute a stock possessing all the general characters 

 of the variety, but with a distinct superiority in pro- 

 ductiveness. 



Above all, the new strain a pure line bred from 

 a single ear will be exceptionally uniform, and, with 

 barley of all plants, uniformity is itself a quality of the 

 highest value. Major Hallett's pedigree barleys were 

 really " pure line " strains, but the rigour of the 

 method was first applied to the production of improved 

 cereals in Sweden and in Denmark. The Danish 

 experimenters, for example, selected a valuable " pure 

 line " of the English barley known as " Archer," and 

 thereby raised the yield of barley in Denmark ; this 

 " Lyngby " or Danish Archer has proved itself, in the 



