“The effect of drainage is not merely to carry off the superfluous water and thus promote the aëration of the soil to the depth reached by the roots; it also keeps the soil cool and moist by the constant presence of water in the drainage ditches or pipes. When a heap of sand is watered at its base, the moisture is seen to mount higher and higher until it reaches the top. In like manner the water collected in our drainage ditches soaks into the upper soil in a dry time and thus reaches the roots of plants growing there, so that water which is superfluous or even harmful at certain periods is held in reserve and gradually distributed at the right moment. “Another advantage of a drainage system is that it prevents that cooling of the soil which would result from prolonged evaporation. In taking the form of vapor water chills the objects that help to promote the evaporation. For this reason we feel a decided chill on emerging from a bath; the film of moisture that covered us is passing off in vaporous form. Similarly a constant evaporation at the surface of a water-soaked tract of land chills the ground and we have a cold soil. But if the water is carried off by proper drainage, evaporation ceases and there is no further chilling of the surface soil. Now, a high temperature is always favorable to vegetation. “Draining is so beneficial that it is not confined to marshy ground, which without it would be quite unproductive, but is applied also to ordinary arable land. Wherever the soil is too clayey, or even where the surface soil is good but the subsoil clayey, rain-water cannot drain off readily and the ground remains soggy and cold. Eventually, however, it dries up, but there being no way for the air to permeate the soil, the latter is left hard and unyielding, so that the roots are by turns drowned in liquid mud and held fast in a tenacious paste that has been baked by the sun. Drainage overcomes these difficulties, and consequently all rich soils that hold rain-water for some time before infiltration are much improved by being properly drained.” CHAPTER XLIII PARING AND BURNING