_Riding Plow._--The riding plow in lifting and turning the furrow slice depends a good deal on the wheels. The action of the plow is that of a wedge with the power pushing the point, the share and the moldboard between the furrow slices and the land side and the furrow bottom. There is the same friction between the moldboard and the furrow slice as in the case of the walking plow, but the wheels are intended to materially reduce the pressure on the furrow bottom and against the land side. Plow wheels are intended to relieve the draft in this respect because wheels roll much easier than the plow bottom can slide with the weight of the work on top. The track made in the bottom of the furrow with the walking plow shows plainly the heavy pressure of the furrow slice on the moldboard by the mark of the slip. To appreciate the weight the slip carries, an interesting experiment may be performed by loading the walking plow with weights sufficient to make the same kind of a mark when the plow is not turning a furrow. One advantage in riding plows in addition to the relief of such a load is less packing of the furrow bottom. On certain soils when the moisture is just sufficient to make the subsoil sticky, a certain portion of the furrow bottom is cemented by plow pressure so that it becomes impervious to the passage of moisture either up or down. The track of a plow wheel is less injurious. [Illustration: Figure 136.--Three-Section, Spike-Tooth Harrow. The harrow is made straight, but the hitch is placed over to one side to give each tooth a separate line of travel.] [Illustration: Figure 137.--Harrow Sled Long Enough to Hold a Four-Section Harrow.] Plow wheels should stand at the proper angle to the pressure with especial reference to the work performed. Wheels should be adjusted with an eye single to the conditions existing in the furrow. Some wheel plows apparently are especially built to run light like a wagon above ground regardless of the underground work required of them. [Illustration: Figure 138.--Corn Cultivator. A one-row, riding-disk cultivator. The ridges are smoothed by the spring scrapers to leave an even surface to prevent evaporation.] Axles should hang at right angles to the line of lift so accurately as to cause the wheels to wear but lightly on the ends of the hubs. Mistakes in adjustment show in the necessity of keeping a supply of washers on hand to replace the ones that quickly wear thin.