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.

It has been urged by Bouyoucos (l) and by Haines (2) that soil granulation is caused by the action of water on lumps of partially dried soil, and it is usually accepted that alternate dryings and wettings are largely responsible for the production of tilth. The work described in this article was undertaken to determine whether measurements of the time required for the complete disintegration by water of lumps of dry soil might furnish a reliable method of soil comparison in accordance with these ideas.

Age, it will be remembered, is here measured in lactations, but little error is involved if the true age in years, at the commencement of the lactation, is taken as two more than the number of the lactation—e.g. a cow, on the average, calves her third calf when she is roughly 5 years old.

1. The relative proportions of exchangeable bases in nine soils from the east of Scotland area and the changes effected by dilute chloride solutions have been examined.

2. The changes due to N/50 solutions are large, and magnesium is displaced to a greater extent by calcium than by potassium.

3. The changes due to N/500 solutions are very small, comparable to what might be expected in manurial practice, and not greater than field sampling error.

4. The content of exchangeable bases and their relative proportions, therefore, seem to be fairly permanent for any soil under normal conditions, but vary considerably from soil to soil, and should prove useful as an additional characteristic of soil type as distinguished in the field.

1. Cultures of B. radicicola derived from eight different host plants have been studied and a description is given of the morphology and reproductive processes of the organisms.

2. The growth forms described include rods, coccoids, branched forms, gonidangia, gonidia and dwarfed growth, and microcysts.

3. The different cell types represent normal stages in the development of the organisms.

4. The reproductive processes described are fission, budding, liberation of gonidia, formation of regenerative bodies, and germination.

5. The formation of symplasm and the regeneration of cells is discussed.

1. The soil temperatures in Egypt at a number of depths have been recorded by means of continuous recording thermometers. In general, the records show that the amplitude of the temperature wave at the surface of the soil is considerably greater than the air temperature wave. There is, however, a considerable damping of the wave with depth, no daily variation in temperature being observed at a depth of 100 cm.

2. No definite relation between the air and soil temperatures could be traced. The maximum air temperature was recorded in May and the maximum soil temperature in July.

3. The amplitude of the temperature wave decreases with increase in depth. The decrease in amplitude of the soil temperature wave is not regular owing to variations in the physical properties of the soil layers. Between any two depths, the ratio of the amplitudes of the temperature waves is constant throughout the year. The amplitude of the soil temperature wave bears no relation to the amplitude of the air temperature wave.

4. The time of maximum temperature at the soil surface is constant throughout the year at 1 p.m. The times of maximum temperature at depths below the surface lag behind the time of surface maximum, but they are constant throughout the year. When plotted against depth, the times of maximum at the various soil depths lie on a straight line.

1. Examinations have been made of the losses involved by igniting fractions of tropical soils.

2. It has been found that these losses are partly due to organic matter and partly to combined water; the greater part of the loss is due to water.

3. In the clay fraction there is a correlation between the amount of combined water and the silica/alumina ratio; the greater the ratio the less the combined water. This is affected by the proportion of iron present.

4. Lateritic soils lose more water on ignition than other soils but the lateritic material in soils is not necessarily evenly distributed throughout the fractions; those fractions containing the highest proportions of lateritic material lose the most water.

1. Of a large number of cultivated soils examined, chiefly from the south-east of Scotland, the majority had a pH between 5 and 6·5, a “lime requirement” of 0·05 to 0·25 per cent. CaCO3 and an exchangeable calcium content of 0·1 per cent, to 0·45 per cent. CaO.

2. A general agreement was observed between these three sets of figures although numerous exceptions occurred.

3. The reaction of a district of six square miles was studied in detail and of a single farm in still greater detail.

4. Long unploughed soils were found to have a low pH, a low content of exchangeable calcium and a high “lime requirement.”

5. Woodland, hill and heath soils were characterised in their surface layers by an extremely low pH (below 5 as a rule), a low content of exchangeable calcium (usually less than 0·1 per cent. CaO) and a high “lime requirement.”

The question of the effect of iodine manuring on the iodine content of plants has recently assumed considerable importance in view of the use of iodine as a cure and preventive of simple goitre. Whether the theory that goitre is due to deficiency of iodine be correct or not, it appears to be well established that small doses of iodine act both as a cure and a preventive of enlargements of the thyroid. It has therefore been suggested that a simple and effective method of general prophylaxis, in areas where goitre is at present endemic, might be found in increasing the iodine content of foodstuffs such as milk and eggs, by administration of iodine, and of plants by iodine manuring.