less draft is required, even when it is carried to a much greater depth. _Underdrainage_, then, must be counted as being among the most effective means both of utilizing the rainfall so as to prevent loss from runoff and injury from washing, and of creating a deep, loose, pervious soil mass, well adapted to root penetration as well as to the conservation of moisture; rendering possible timely tillage and cultivation, and early development of crops fully supplied with moisture and therefore secure against loss from drought. The safety and improvement of crops thus secured corresponds in the humid region to that brought about by the command of irrigation water in the arid countries. But it by no means follows that underdrainage can therefore be dispensed with in the latter, or irrigation in the former. Both have their proper place in both regions; but from special causes underdrainage, as has already been stated, should be widely used in irrigation countries to prevent the injuries otherwise but too likely to arise from over-irrigation (see chap. 12, p. 231). _Winter Irrigation._—In many regions where irrigation is desirable but not absolutely necessary in ordinary seasons, or where irrigation water is scarce in summer, much advantage is gained by insuring thorough saturation of the land during the latter part of winter, especially when spring or summer crops are to be sown. The not inconsiderable time required for water to reach its permanent level or the country drainage in most soils, often insures the retention of a certain surplus over what the soil can permanently hold, within the period when it can be utilized by growing crops; whose roots moreover are more likely to penetrate deeply in land where there is a steady increase of moisture as they descend, than when the contrary condition is encountered. The use of _winter flood-waters to saturate the land_ is therefore in many cases the saving clause for a dry season. METHODS OF IRRIGATION.[89] The manner in which irrigation water is supplied to land and especially to growing crops exerts such a potent influence not only upon the welfare of the plants but also upon the condition of the land, that a brief discussion of this topic seems necessary. The following methods are in use to a greater or less extent: 1. Surface sprinkling. 2. Flooding. A. By lateral overflow from furrows or ditches. B. By the “check” system. 3. Furrow irrigation. 4. Lateral seepage from ditches. 5. Basin irrigation. 6. Irrigation from underground pipes. [89] Only a general outline of the principles of this subject is given in this volume; special works must be consulted for working details. Among these the volume by King on “Irrigation and Drainage” gives probably the most comprehensive presentation of the subject for both humid and arid climates. Also bulletins of the U. S. Dep’t of Agriculture.