Ploughs are of various kinds. The coulter[350] is the iron part that cuts up the dense earth before it is broken into pieces, and traces beforehand by its incisions the future furrows, which the share, reversed,[351] is to open out with its teeth. Another kind—the common plough-share—is nothing more than a lever, furnished with a pointed beak; while another variety, which is only used in light, easy soils, does not present an edge projecting from the share-beam throughout, but only a small point at the extremity. In a fourth kind again, this point is larger and formed with a cutting edge; by the agency of which implement, it both cleaves the ground, and, with the sharp edges at the sides, cuts up the weeds by the roots. There has been invented, at a comparatively recent period, in that part of Gaul[352] known as Rhætia, a plough with the addition of two small wheels, and known by the name of “plaumorati.”[353] The extremity of the share in this has the form of a spade: it is only used, however, for sowing in cultivated lands, and upon soils which are nearly fallow. The broader the plough-share, the better it is for turning up the clods of earth. Immediately after ploughing, the seed is put into the ground, and then harrows[354] with long teeth are drawn over it. Lands which have been sown in this way require no hoeing, but two or three pairs of oxen are employed in ploughing. It is a fair estimate to consider that a single yoke of oxen can work forty jugera of land in the year, where the soil is light, and thirty where it is stubborn. CHAP. 49. (19.)—THE MODE OF PLOUGHING. In ploughing, the most rigid attention should be paid to the oracular precepts given by Cato[355] on the subject. “What is the essence of good tillage? Good ploughing. What is the second point? Ploughing again. What is the third point? Manuring. Take care not to make crooked furrows. Be careful to plough at the proper time.” In warm localities it is necessary to open the ground immediately after the winter solstice, but where it is cold, directly after the vernal equinox: this, too, should be done sooner in dry districts than in wet ones, in a dense soil than a loose one, in a rich land than a meagre one. In countries where the summers are hot and oppressive, the soil cretaceous or thin, it is the best plan to plough between the summer solstice and the autumnal equinox. Where, on the other hand, the heat is moderate, with frequent falls of rain, and the soil rich and full of vegetation, the ploughing should be done during the prevalence of the heat. A deep, heavy soil, again, should be ploughed in winter; but one that is very thin and dry, only just before putting in the seed.