— 69 — All the seedlings placed outside died so soon after germination that no determinations were made, but the wilting point must be higher.

Eoot limitation is, in the writer's opinion, responsible for much of the straggly stunted cotton that exists on heavy clay soils in the Northern Sudan.

Roots that have been dug up from such soils showed little lateral development, and had not penetrated much below a metre.

On lighter soils the cotton is much more luxuriant, and the root system correspondingly well developed.

Salt, Drainage and Attendant Problems.—The experimental area of the Central Research Farm is too small and too isolated to furnish figures with reference to the permanent accumulation of irrigation water, but it has been shown that water tends to accumulate about 2 metres, at which depth serious damage may be inflicted on the cotton plant should saturation occur, or an excess of salts appear.

Conditions favourable to the development of alkali exist in all arid countries. Indeed the extraordinary fertility of some arid soils when irrigated is due to the large percentage of soluble salts which have not been washed into the subsoil by rain. It must be remembered that the water supplied to the land also contains salts in solution which are left behind in the soil as the water evaporates, and even if the excess of the irrigation water should continue to penetrate to depths at which no harm can be done to the crop this water will eventually be brought to the surface, by capillarity, richer than ever in soluble salts, and thus in a short time the surface layers will be rendered unsuitable for agriculture.

The only remedy for this evil is drainage. It has been abundantly proved in India, Africa and the United States that irrigation without adequate drainage must ultimately end in failure.

During the past three years a nunaber of analyses have been made of the salt contained in the farm soils, and also of the drainage water resulting from the irrigation of these soils.

Composition of Irrigation Water.—To permit of logical sequence, an examination was first made of the river water supplied to the farm. The pumping station is situated between three and four miles below the junction of the White and Blue Nile, and so receives water from both sources in a proportion which varies with the time of year.

As might be expected considerable changes in composition occur according to the state of the river, but the most noteworthy feature is the increase in the