Thus while in some very pervious land furrows may be six or even eight feet apart, in other cases, in certain finely pulverulent or silty soils such as the “dust soils” described in a former chapter; (see chapter 6, p. 104), furrows drawn three feet apart may fail to allow the water to penetrate so as to prevent grain on the middle foot from suffering from drought after the water has run for twenty-four hours. _Irrigation by lateral Seepage._—Is in reality a mere modification of furrow irrigation, practiced in the case of lands very readily permeable, and where water is abundant. The fields are laid off in “lands” twelve to twenty-five feet wide, with a deep furrow or narrow ditch between, from which water percolates in a short time so as to overlap from the two sides. In this case sometimes the water does not reach the surface visibly at all; a very great advantage where alkali exists, as surface evaporation, and the consequent accumulation of alkali, is thus effectually prevented; while deep-rooting is favored to the utmost. _Basin Irrigation._—In this method of irrigation, practiced only in the case of trees and sometimes vines, and when water is scarce, a wide circular furrow or basin is excavated around each trunk and water is run either from one to the other, or sideways from a furrow laid along the rows. The water thus applied of course percolates immediately around the trunk first, and in practice is found to follow also the large roots; so that it goes precisely where it is most wanted, besides forming a vertical body of moist soil reaching to considerable depth, where it is most desirable that the root system should follow. By this deep penetration to natural moisture in the depths of the soil, comparatively small quantities of water produce very marked effects. On the same principle, the grape vines which bear some of the choicest raisins of Malaga on the arid coastward slopes, are made to supply themselves with moisture, without irrigation, by opening around them large, funnel-shaped pits, which remain open in winter so as to catch the rain, causing it to penetrate downward along the taproot of the vine, in clay shale quite similar to that of the California Coast Ranges, and like the latter almost vertically on edge. Yet on these same slopes scarcely any natural vegetation now finds a foothold. Similarly the “ryats” of parts of India water their crops by applying to each plant immediately around the stem such scanty measure of the precious fluid as they have taken from wells, often of considerable depth, which form their only source of water-supply. Perhaps in imitation of these, an industrious farmer has practiced a similar system on the high benches of Kern River, California, and has successfully grown excellent fruit for years, on land that would originally grow nothing but cactus. Sub-irrigation from pipes has been applied in a similar manner.