In this respect a good deal depends on the sand-bands at the ends of the hubs. Plow wheels are constantly lifting gritty earth and dropping it on the hubs. There is only one successful way to keep sand out of the journals and that is by having the hubs, or hub ferrules, extend well beyond the bearings. Plow wheel hub extensions should reach two inches beyond the journal both at the large end of the hub and at the nut or linchpin end. Some plow wheels cut so badly that farmers consider oil a damage and they are permitted to run dry. This is not only very wasteful of expensive iron but the wheels soon wabble to such an extent that they no longer guide the plow, in which case the draft may be increased enormously. [Illustration: Figure 139.--A Combination Riding and Walking Cultivator, showing fenders attached to protect young plants the first time through. The two bull tongues shown are for use in heavy soils or when deeper digging is necessary.] _Scotch Plows._--When the long, narrow Scotch sod plows are exhibited at American agricultural fairs they attract a good deal of attention and no small amount of ridicule from American farmers because of the six or seven inch furrows they are intended to turn. In this country we are in too much of a hurry to spend all day plowing three-fourths of an acre of ground. Intensive farming is not so much of an object with us as the quantity of land put under cultivation. Those old-fashioned Scotch plows turn a furrow about two-thirds of the way over, laying the sod surface at an angle of about 45° to the bottom of the furrow. The sharp comb cut by the coulter and share stands upright so that a sod field when plowed is marked in sharp ridges six or seven inches apart, according to the width of the furrow. Edges of sod show in the bottoms of the corrugations between these little furrow ridges. When the rains come the water is held in these grooves and it finds its way down the whole depth of the furrow slice carrying air with it and moistening every particle of trash clear to the bottom of the furrow. Such conditions are ideal for the work of the different forms of bacteria to break down plant fibre contained in the roots and trash and work it into humus, which is in turn manipulated by other forms of soil bacteria to produce soil water which is the only food of growing plants.