In any field of corn the population-density or number of plants per unit length of row is very fluctuating. Accidental circumstances may result in considerable stretches being empty or thinly populated. Quite apart from this, the population of successive short lengths is sharply and characteristically inconstant. Where plants are few tillering is profuse and there is thus a tendency towards constancy in yield per unit length of row. Specific ascertainment has, in earlier experiments, suggested that the tendency is by no means marked. In consequence fluctuation of population-density in the sense here used, reduces yield in typical field crop substantially below the potential maximum appropriate to the soil and other circumstances. From short lengths of row, low in plant-population, yields are low. In aggregate these sparsely populated lengths are a feature of considerable economic importance.