The agricultural conception, yield, piquantly clear to farmers, has evaded statistical analysis and confounded plant physiology. It may be defined for cereals as the average weight of grain produced per unit area. Grain is an end-product of the operation throughout the plant's life, of all its vital processes. Yield therefore, in some complex way, must reflect the working of these processes. An analysis of yield would simplify the testing of new plant forms and regularise the selection of parents in hybridising. Fundamentally this analysis should comprise the identification of the vital processes of the plant, the effects upon them of environmental factors, and their relationship to grain production. At present even to speculate upon the making of such an analysis would be mere pedantry. Nothing but an algebraic analysis is practicable.