As a matter of fact, if we put aside those gardeners who chiefly cultivate the so-called _primeurs_--strawberries ripened in January, and the like--if we take only those who grow their crops in the open field, and resort to frames exclusively for the earlier days of the life of the plant, and if we analyse their system, we see that its very essence is, first, to create for the plant a nutritive and porous soil, which contains both the necessary decaying organic matter and the inorganic compounds; and then to keep that soil and the surrounding atmosphere at a temperature and moisture superior to those of the open air. The whole system is summed up in these few words. If the French _maraîcher_ spends prodigies of labour, intelligence, and imagination in combining different kinds of manure, so as to make them ferment at a given speed, he does so for no purpose but the above: a nourishing soil, and a desired equal temperature and moisture of the air and the soil. All his empirical art is devoted to the achievement of these two aims. But both can also be achieved in another and much easier way. The soil can be _improved_ by hand, but it need not be _made_ by hand. Any soil, of any desired composition, can be made by machinery. We already have manufactures of manure, engines for pulverising the phosphorites, and even the granites of the Vosges; and we shall see manufactures of loam as soon as there is a demand for them. It is obvious that at present, when fraud and adulteration are exercised on such an immense scale in the manufacture of artificial manure, and the manufacture of manure is considered as a chemical process, while it ought to be considered as a physiological one, the gardener prefers to spend an unimaginable amount of labour rather than risk his crop by the use of a pompously labelled and unworthy drug. But that is a social obstacle which depends upon a want of knowledge and a bad social organisation, not upon physical causes.[63] Of course, the necessity of creating for the earlier life of the plant a warm soil and atmosphere will always remain, and sixty years ago Léonce de Lavergne foretold that the next step in culture would be to warm the soil. But heating pipes give the same results as the fermenting manures at a much smaller expense of human labour. And already the system works on a large scale, as will be seen from the next chapter. Through it the productive powers of a given area of land are increased more than a hundred times.