There exists a great amount of genetic diversity and of free as well as potential variability among and within the familial lines. Consequently, natural selection acting through heterozygote advantage and differential competing ability has often sufficient plasticity in the genetic composition to mould into better adaptive types. Whether fitness and agronomic productivity of a bulk population are improved simultaneously would depend upon the relationship between the two genetic systems governing them. In case of a linear correlation such as one observed in the barley material studied, the bulk method seems to be quite promising, particularly in view of the great economy in cost and labour involved in the entire program. Another important feature is, at least on theoretical grounds, the greater stability in the performance of a mixed population owing to a wider adaptive base against different environments, or such adverse factors as a coevolving group of some pathogenic races. However, it appears that progress under natural selection is perhaps too slow and therefore, artificial selection might also be resorted to at suitable stages in the bulk program on the basis of usual testing and evaluating procedures. Isolation of superior familial lines by the F10 or F15 generation followed by their separate bulk propagation might prove an efficient scheme.
*) Now at the Division of Botany, I.A.R.I., New Delhi 12, India.