From the preceding paper in this issue it is clear that the topography and the climate of the Netherlands necessitate a permanent struggle to keep out water, on the one hand, and to supply water on the other. That paper deals with control in open waterways (main drainage) ; this paper deals with the corresponding tile drainage and with subirrigation. The ground-water level of much of the Netherlands is high. In many regions it is at a depth of 0.5 m. in winter and of 1 to 1.5 m. in summer. A considerable part of the Netherlands, it must be remembered, is below sea level (fig. 1). In the higher sandy areas in the east the water table is several meters deep in many places, and in the loess soils of southern Limburg, more than 100 m. above sea level, it is more than 10 m. deep. About 1845, mechanical tile-making in England paved the way for the application of tile drainage for land improvement on a large scale. In the Netherlands the first tiles were laid in 1852. Subirrigation was started much later, about the 1920's. Since then, the drained regions have been extended considerably (fig. 2). Subirrigation has made much slower progress. A comparison of figure 2 with Edelman's new soil map of the Netherlands (5) shows that tile drainage has been applied almost exclusively to the heavier soils. Subirrigation, on the other hand, is used mainly on sandy soils, though peaty and even clayey soils (grassland) are now being subirrigated. Arable land, especially, is tile-drained; grassland, as well as some horticultural land, is subirrigated. This is because arable land is less subject to drought than is permanent grassland, though grassland should not be too wet in spring. It follows that tile drainage and subirrigation are closely related and therefore can be best discussed together. Both aim to control the ground-water level, but in opposite directions (fig. 3). Tile drainage and systematic subirrigation are not necessary with open waterways (usually ditches 100 to 300 m. apart), provided the soil is sufficiently permeable to an adequate depth. For subirrigation, the level of the ditches should be raised to about 40 cm. below the surface. For good drainage, the water level should generally be lower than 1 m. Where the permeability of the soil is low, tile drainage or systematic subirrigation will be necessary. In the Netherlands, tile drainage, mole drainage, and trenching by means of shallow ditches are used, the last almost exclusively for subirrigation. In subirrigation, the level of the trenches and of the ditches into which the tiles or the