AGRICULTURAL CHEMISTRY AND GEOLOGY. 179 



are lost in the magnitude of the processes by which nature works ; but we see the more 

 clearly that, on such a scale, the quantity of material supplied by the air, though minute to 

 the individual, becomes vast in the aggregate. We see, moreover, the necessity for under- 

 standing the relations between evaporation and rate of growth, and the laws and effects of 

 absorption in soils. A thousand pounds of dry calcareous sand will gain two pounds in 

 weight in twelve hours when the air is moist, while pure agricultural clay will gain thirty- 

 seven pounds. 



The source of nitrogen comes next to be considered ; and this also is seen to be independent 

 of manures. Hereupon, it is observed that "our domestic plants do not require a greater 

 supply than in a state of nature. A water-meadow which has never received any dung, 

 yields yearly from forty to fifty pounds of nitrogen, while the best plowed land yields only 

 about thirty-one pounds. The plants for which most dung is used, as potatoes and turnips, 

 are in fact proportionally the poorest in nitrogen." That there is a supply independent of 

 the soil, is further seen in the millions of hides furnished every year by the cattle of the 

 Pampas, without any diminution of produce; and in the great quantities of nitrogenous 

 matters, hay, butter, and cheese, carried off from pasture-land ; far more than is returned by 

 the animals fed thereon. Experiments with various kinds of plants on various soils have 

 satisfactorily demonstrated that increase of nitrogen in the land and in the crop does take 

 place, quite irrespective of supplies of manure. 



With respect to ammonia, "it appears that one-thirteenth of a grain in every pound of 

 water is sufficient for the exigencies of vegetation, and there is perhaps no spring-water in 

 the universe which contains so little." Then as to sulphur and phosphorus, which are also 

 among the constituents of plants, the quantity needed in proportion to the time of vegetation 

 is so small, that 540,000th of a grain of sulphuretted hydrogen per cubic foot, diffused 

 through the atmosphere to a height of 3000 feet, is all that is required. 



The consideration that cereals would soon disappear from the north of Europe, if not culti- 

 vated, and perhaps from nearly the whole of this quarter of the globe, adds weight to the 

 arguments in favor of enlightened attention to the inorganic constituents of plants. The 

 point is to bring the soil into harmony with the conditions by which growth may best be pro- 

 moted. Much depends on the nature of the soil ; the darkest-colored lands are generally the 

 highest in temperature ; hence the advantage of vegetable mould ; while deep, light sands, 

 and clay, which turns almost to stone in dry weather, weary and vex the cultivator by their 

 unprofitableness. It is to be remembered, however, that soils which have the highest tem- 

 perature of their own, may not be those most susceptible of receiving heat — that is, from 

 the sun, because some lands are warmed by the springs that irrigate them. Here we have 

 an explanation of the phenomena of certain soils which are warm in winter and cool in sum- 

 mer. The application of humus evolves heat by the process of combustion ; and sand, lime, 

 clay, and humus are the combinations needed, the clay being in a proportion of from 40 to 

 50 per cent. ; if less than 10 per cent., the land will be too light and poor. 



Although Schleiden's views apply chiefly to the practice of German agriculturists, they 

 will be found to bear on the whole science of cultivation. In summing up, he insists strongly 

 on the necessity for selecting good seed ; that from a barren soil, he observes, is likely to be 

 more true to its kind than from well-manured land. Also, that the time of sowing should be 

 adapted to the requirements of the plant; rye and barley, for instance, should be sown in 

 drier weather than oats. And it will surprise many to read that he advocates a less frequent 

 use of the plow. He holds plowing to be a "necessary evil, one to be employed only so far 

 as necessity requires;" because, by the too frequent loosening of the soil, the decomposition 

 of humus is so rapid as to overbalance the benefit supposed to arise from exposure to the 

 atmosphere. He shows, too, that covered fallows are in most cases preferable to naked 

 fallows, as the latter tend to waste the valuable qualities of the soil; while, in a field sown 

 with clover, the quantity of humus and carbonic acid is increased by the leaves preventing 

 evaporation. Naked fallowing is to be adopted only when the soil cannot be loosened in any 

 other way; but there is to be no stand-still; "the notion of rest, so prevalent among culti- 

 vators, is clearly wrong, except it be rest from the destructive influence of the plow:" and 

 always must it.be borne in mind "that manures do not act immediately on vegetation by 



