2. _They are not permanent._ A properly laid underdrain will last half a century or more, but an open drain, especially if deep, has a constant tendency to fill up. Besides, the action of frost and water and vegetation has a continual operation to obstruct open ditches. Rushes and water-grasses spring up luxuriantly in the wet and slimy bottom, and often, in a single season, retard the flow of water, so that it will stand many inches deep where the fall is slight. The slightest accident, as the treading of cattle, the track of a loaded cart, the burrowing of animals, dams up the water and lessens the effect of the drain. Hence, we so often see meadows which have been drained in this way going back, in a few years, into wild grass and rushes. 3. _They obstruct good husbandry._ In the chapter upon the effects of drainage on the condition of the soil, we suggest, in detail, the hindrances which open ditches present to the convenient cultivation of the land, and, especially, how they obstruct the farmer in his plowing, his mowing, his raking, and the general laying out of his land for convenient culture. 4. _They occupy too much land._ If a ditch have an upright bank, it is so soft that cattle will not step within several feet of it in plowing, and thus a strip is lost for culture, or must be broken up by hand. If, indeed, we can get the plow near it, there being no land to rest against, the last furrow cannot be turned from the ditch, and if it be turned into it, must be thrown out by hand. If the banks be sloped to the bottom, and the land be thus laid into beds or ridges, the appearance of the field may, indeed, be improved, but there is still a loss of soil; for the soil is all removed from the furrow, which will always produce rushes and water-grass, and carried to the ridge, where it doubles the depth of the natural soil. Thus, instead of a field of uniform condition, as to moisture and temperature and fertility, we have strips of wet, cold, and poor soil, alternating with dry, warm, and rich soil, establishing a sort of gridiron system, neither beautiful, convenient, nor profitable.