SOILS AND FERTILIZERS and distilled water. After five years he pulled up the willow and it now weighed 169 pounds and 3 ounces." * He concluded that 164 pounds of roots, bark, leaves, and branches had been produced by the direct transmutation of the water. It is evident from the preceding example that anything like an adequate idea of the growth and composition of plant bodies could not be gained until the composition of air and water was established. The discovery of oxygen by Priestly, in 1774, of the composition of water by Cavendish in 1781, and of the role which carbon dioxide plays in plant and animal life by DeSaussure and others in 1800, form the nucleus of our present knowledge regarding the sources of matter stored up in plants. It was between 1760 and 1800 that alchemy lost its grip, because of advances in knowledge, and the way was opened for the development of modern chemistry. The work of DeSaussure, entitled " Recherches sur la Vegetation," published in 1804, was the first systematic work showing the sources of the compounds stored up in plant bodies. He demonstrated, quantitatively, that the increase in the amount of carbon, hydrogen, and oxygen, when plants were exposed to sunlight, was at the expense of the carbon dioxide of the air, and of the water of the soil. He also maintained that the mineral elements derived from the soil were essential for plant growth, and gave the results of the analyses of many plant ashes. He believed that the nitrogen of the soil was the main source of the nitrogen found in plants. These views have since of investigating the composition and of the study of the character of the different substances from which plants derive their nourishment." 3 Soon after Liebig's first work appeared, the investigations at Rothamsted by Sir J. B. Lawes were undertaken. The most extensive systematic work in both field experiments and laboratory investigations ever conducted have been carried on by Lawes and Gilbert 10 SOILS AND FERTILIZERS weight. But when saturated with water, a cubic foot of peaty soil weighs more than a cubic foot of sandy soil. Clay soils weigh less per cubic foot than sandy soils. The larger the amount of organic matter in a soil the less the weight. Pasture land, for example, weighs less per cubic foot than arable land. Weight is an important property to consider when the total amounts of plant food in two soils are compared. A peaty soil containing i per cent, of nitrogen and weighing 30 pounds per cubic foot has less total nitrogen than a soil containing 0.40 per cent, of nitrogen and weighing 80 pounds per cubic foot. The weight of soils per cubic foot is approximately as follows : 5 Pounds.
