Plant breeding, which in 1936 was a simple art depending on serendipity and the breeder's instinct, had become, by the end of our fifty-year period, a highly sophisticated application of the science of botany to the manipulation of the plant's genetic capacity. Botany itself has evolved over the same period into a number of rapidly advancing branches of pure science, plant genetics, physiology, biochemistry, pathology, molecular genetics, morphology, cytology and taxonomy; parts of each of these have become sharply focused on the practical problem of improving crop plants for human use. As the science has increased in power, so that there is scarcely any goal that seems beyond reach, countervailing forces from the inertia of the agricultural market, with its capacity to evaluate the weaknesses as well as the strengths of apparently promising varieties, have increased.

Advances in plant breeding have taken place world-wide, but in this chapter work undertaken in the United Kingdom will be discussed particularly, because the complex interactions between breeding and agricultural change can be understood best on the smaller canvas.

British agriculture in our revolutionary period has utilised a very limited number of crops. Wheat and barley were the major cereals throughout; the oat crop was important at the beginning of the period but has since declined rapidly; rye has never been of other than limited importance on light dry soils. Cash crops were represented by sugar beet and potatoes.