A regular optimum spacing among plants is the theoretical ideal. Regularity is difficult to secure and the ever varying optimum is not determinable. But earlier investigations have shown that field crops of corn are marked by extremely high fluctuation in population density along the rows of plants; and further, that in this fluctuation lies an important limitation to potential yield. Wider knowledge of this limitation is being sought. The experiments have clearly confirmed plant density fluctuation as a characteristic of field crops (of wheat). Measures of this fluctuation and analyses of its nature and causes are the subject of the paper.

In relation to plant development and yield, fluctuations in density or spacing from point to point along the row, are the most important features associated with drill action. These have been measured by counts, both of seeds and of plants, on unit lengths of row. Such “census” counts are described in detail for four normal fields. Plant counts were made periodically. In general a unit length of one foot of row was adopted. For analytical purposes the refinement of a per-inch count proved necessary.

Fluctuation in seeds deposited per foot may be illustrated by the data from one of the fields. The mean was 18·0 and the standard deviation was 7·2. In aggregate the field could be regarded as consisting of five equal portions (quintiles of the per-foot distribution) for which:

Number of seeds per foot = 5·0–12·2; 12·2–15·0; 15·0–18·0; 18·0–22·3.

Equivalent seeds rates (bushels per acre) = 1·42; 2·00; 2·35; 3·11; 3·70.

The distribution per inch, determined by a specially devised method, is illustrated for two fields in Diagram I. Four equal aggregates (quintiles of per-foot distribution) from one and the same acre had the widely different seedings displayed in Diagrams II and III.