“Finally, the operation just described affects the soil through the ashes of the burnt weeds. After the combustion of all vegetable matter there remains an earthy powder or ash comprising the mineral substances contained in that vegetable matter, substances unchanged by combustion because of their great resistance to heat. The most important of these is potash. All the ingredients that once belonged to the burnt plants are evidently adapted to the formation of new plants. The ashes, then, of the weeds consumed in the process of paring and burning will be very useful to the plants about to be raised on the land that has been burnt over. By the burning, however, it is impossible to turn to account all that the weeds contained: what escapes in the form of smoke is so much lost. Hence care should be taken not to carry combustion too far. In this connection the calcined clay renders still another service. By becoming porous through calcination its nature is altered so that it can absorb and retain the gaseous products of combustion and thus save just so much waste. But if a soil lacks clay, paring and burning are harmful, and it is better simply to turn the weeds under, whereupon they will be converted into mold instead of being dissipated in the atmosphere as smoke. “Ashes other than those resulting from paring and burning are also used as an agricultural fertilizer, though they are rarely put to this use just as they are, because the contained potash, a highly valuable substance, is first extracted by leaching. After this process the ashes are called buck-ashes. They contain silica and also carbonate and phosphate of lime, all in a condition most favorable for assimilation by plants. Of less strength than ordinary ashes, leached ashes nevertheless produce good results, especially on clayey soil. Coal ashes, too, it should be added, serve to lighten a heavy soil since they contain a large proportion of calcined clay. “The subject of ashes leads us naturally to that of soot, a substance composed of vegetable matter incompletely decomposed by heat and containing ammonia, which renders it highly efficacious as a fertilizer. It is applied to young plants, giving them an increased vigor of growth. By its acrid quality, moreover, it is excellent as a protection against insects that attack vegetation.” CHAPTER XLIV WINE-MAKING