As to the supposed more complete use of the soil under the latter two methods, it must be remembered that while this is the case in a _horizontal_ direction, if irrigation is practiced too copiously under the shallow-furrow system, it may easily happen that the gain made horizontally is more than offset by a corresponding loss in the _vertical_ penetration of the root-system. This is amply apparent in some of the irrigated orange groves of southern California, where the fine roots of the trees fill the surface soil as do the roots of maize in a corn field of the Mississippi States; so that the plow can hardly be run without turning them up and under. In these same orchards it will often be observed, in digging down, that at a depth of a few feet the soil is too water-soaked to permit of the proper exercise of the root-functions, and that the roots existing there are either inactive or diseased. That in such cases frequent irrigation and abundant fertilization alone can maintain an orchard in bearing condition, is a matter of course; and there can be no question that a great deal of the constant cry for the fertilization of orchards in the irrigated sections is due quite as much to the shallowness of rooting induced by over-irrigation, as to any really necessary exhaustion of the land. When the roots are induced to come to and remain at the surface, within a surface layer of eighteen to twenty inches, it naturally becomes necessary to feed these roots abundantly, both with moisture and with plant-food. This has, as naturally, led to an overestimate of the requirements of the trees in both respects. Had deep-rooting been encouraged at first in the deep soils of the southern “citrus belt,” instead of over-stimulating the growth by surface fertilization and frequent irrigation, some delay in bearing would have been compensated for by less of current outlay for fertilizers, and less liability to injury from frequently unavoidable delay, or from inadequacy, of irrigation. _Irrigation by Underground Pipes._—Where economy in the use of irrigation water is a pressing requirement, its distribution through underground pipes affords the surest mode of accomplishing that end, in connection with the application of the water in accordance with the principles just discussed. The enormous saving of water effected by its conveyance in cement-lined ditches or concrete pipes, as compared with earth ditches, if additionally combined with its application to individual trees or vines, presents the maximum of economy that can be effected. The actual use of this method is unfortunately limited in practice by the high first cost of piping; but as its use renders unnecessary the digging of basins and plowing of furrows and their subsequent closing-up, it is when once established by far the cheapest system, both as to the use of water and of labor.