MODERN PLANT-BREEDING METHODS 717 



If a knowledge of Mendel's laws of inheritance will enable 

 one to handle such an indefinite characteristic as the quality of 

 the grain of wheat, in spite of our ignorance of the factors which 

 determine this quality, there can be little doubt that the plant 

 breeder now has his subject more under control than even the 

 most optimistic could have hoped for some few years ago. The 

 mere fact that one can with certainty solve problems of this 

 kind where the majority of previous attempts have been failures 

 is not without its moral value, and it tempts the breeder to apply 

 his methods to equally abstruse characters. Most of the im- 

 provements wHich will be effected as time goes on will be 

 concerned with features of this kind, which offer problems the 

 haphazard methods of the immediate past gave one little hope of 

 attacking with any prospect of success. 



Disease Resistance 



Such a feature is that of disease resistance. To breed disease- 

 resisting plants has always been one of the problems which has 

 appealed to- the small band of workers who have concerned 

 themselves with plant-improvement. Knowing that crossing 

 "broke the type," they have raised numerous hybrids in the 

 hope of finding amongst the progeny some free from the ills 

 the parents were subject to. Looking back at the existing 

 records, the Mendelist often sees clearly where their experiments 

 were bound to fail, for this character was not necessarily present 

 in the plants they used as parents. 



Experiments to test the possibility of raising disease-resisting 

 wheats and barleys have been in progress for some five seasons, 

 with results which indicate that the problem is far from being 

 hopeless. For the most part they have been concerned with the 

 yellow rust, Puccinia glitmarum, this being the commonest and 

 the most serious cereal disease in this country. In other parts 

 of the world the rusts, again, are, on the whole, the most serious 

 of the diseases of these crops, and in some districts an epidemic 

 is such a certainty that it is useless to attempt their cultivation. 

 The rusts sometimes belong to different species from the one with 

 which the experiments to be recorded were carried out, but 

 from trials already made it would appear that the problem is the 

 same for all. 



A variety immune to the yellow rust under the ordinary 



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