The SEVENTH LECTURE is devoted to the investigation of manures of a mineral origin. He commences the subject by refuting the opinion of Schrader and Braconnot, that the different earthy and saline substances found in plants arise from new arrangements of the elements of air and water, by the agencies of their living organs. In 1801, he made an experiment on the growth of oats, supplied with a limited quantity of distilled water, in a soil composed of pure carbonate of lime. The soil and the water were placed in a vessel of iron, which was included in a large jar, connected with the free atmosphere by a tube, so curved as to prevent the possibility of any dust, or fluid, or solid matter, from entering into the jar. His object was to ascertain whether any siliceous earth would be formed in the process of vegetation; but the oats grew very feebly, and began to be yellow before any flowers formed. The entire plants were burnt, and their ashes compared with those from an equal number of grains of oat. Less siliceous earth was given by the plants than by the grains; but their ashes yielded much more carbonate of lime. Numerous other authorities might be quoted to the same effect. Jacquin states that the ashes of Glasswort (_Salsola-Soda_) when it grows in inland situations, afford the vegetable alkali; but when on the sea-shore, the fossile or mineral alkali. Du Hamel also found, that plants which usually grow on the sea-shore, made small progress when planted in soils containing little common salt. The Sunflower, when growing on lands not containing nitre, does not afford that substance; though when watered by its solution, it yields nitre abundantly. De Saussure made plants grow in solutions of different salts; and he ascertained that, in all cases, certain portions of the salts were absorbed by the plant, and found unaltered in their organs. It may be admitted then as established, that the mineral principles found in plants are derived from the soils in which they vegetate. This fact becomes the foundation of the theory respecting the operation of mineral manure. Davy observes, that "the only substances which can with propriety be called fossile manures, and which are found unmixed with the remains of any organized beings, are certain alkaline earths, or alkalies, and their combinations." If he intends to limit the term to those bodies only which find their way into the structure of plants, his definition may be correct; but I am inclined to take a much wider view of the subject, and to include all those mineral substances which promote vegetation by modifying the texture of the soil:--but of this hereafter. Lime, not only from its importance, but from the controversies which it has occasioned, ranks first in the list of mineral manures.