The use of improved strains of seeds has been one of the chief methods of increasing the production of crops. Improved strains of seeds are evolved at the Research Stations by various methods. There are many difficulties encountered at the several stages of building up a strain. With knowledge of the behaviour of the genes and transmission of charecters and improved plant breeding technique, various charecters are combined and suitable strains are evolved. Perhaps the greater difficulty appears after a strain is evolved. Its purity requires to be maintained at a high level, for realisation of the full potentialities of the improved strains. The evolution of the strains is done at the Research Stations and laboratories, where the plant material and the various cultivation operations are under control. The multiplication and spread of the strains in the cultivator's field are under conditions, over which effective control is not possible for various reasons,
SUBBIAH MUDALIAR V.T (Thu,) studied this question.