THE ATMOSPHERIC SOURCE OF VEGETABLE NUTRITION. Dr. William Odling, F.R.S., in the first of twelve lec tures on “ The Chemistry of Vegetable Products,” said that from an acre of meadow land some 4,000 pounds weight of hay is usually removed, as the product of a few months’ growth; and this great quantity of matter has to be traced back to its source. All vegetable pro ducts, when subjected to a moderate heat, out of contact with air, give a considerable quantity of charcoal or carbon, retaining very nearly the outward form of the original substance. In this way evidence is obtained of the presence of carbon in vegetable products of all kinds. The proportion of carbon in wood, corn, wheat, and diffcrent vegetable substances varies, but it averages about 45 or 50 per eent. of the whole weight. When such an enormous weight of carbon is removed from cultivated land every year, the question arises, “ Where Up to about forty does it come from originally?" years ago, the prevailing idea was that it came from decaying and dead vegetable matter in the soil, in the form of a brown substance called “humus." The vegetable mould of forest land contains about 70 per cent. of carbon ; in grass and arable land there is also much humus rich in carbon, and to this substance the origin of vegetable tissue was as scribed. This view was adopted both by Sir Hum phrey Davy and Berzelius, and it was not over thrown till Liebig, in 1840, brought the question under the notice of the British Association; he then heaped proof upon proof that humus was not the source of the carbon in question, and he brought out what is known as “the mineral theory of vegetable nutrition." Before humus can enter a plant it must be dissolved; and Liebig showed that humus is very in soluble in water; also that, if the whole of the rainfall upon an acre of land dissolved all the humus it could take up, and the whole of this humus was carried into the plant during the period of its growth, it would only account for a very small percentage of the carbon in the full-grown vegetable. Humus is, however, more soluble in alkaline liquids, and Liebig proved that if al the alkali contained in plants had been employed to aid the rain water in dissolving humus, still it would not account for a tithe of the carbon found in the plants. Where, then, does the carbon come from? It must come from water, earth, or air; and as water contains, no carbon, attention was drawn to air. Common air contains carbonic acid gas in small proportion, there being about four volumes of the gas to every 10,000 volumes of air. It was found by experiment that peas could be grown in soil consisting only of powdered burnt brick, quite free from organie matter : also in Chili, Peru, and other countries, vegetation is sometimes very rich upon sandy soils, containing The palm trees of the West little or no carbon. Coast of Africa, which grow upon a sandy soil, yielded between the years 1821 and 1830 no less than 107,000,000lbs of oil, containing 32,000 tons of carbon. Where did all the carbon come from ? Although there are only, on an average, four volumes of carbonic acid gas in 10,000 volumes of air, yet that would give a volume of the gas in the theatre of the Royal Institution half as large as the lecture table, and a volume of solid charcoal as big as a brick ; so that when the enormous volume of the atmosphere of the earth is considered, there is plenty of charcoal in it. On every square foot of the surface of the earth there is a column of air pressing with a force of 2,000lbs.; and this column contains about half a pound of charcoal ; calculation, therefore, shows that the atmosphere of the whole earth contains 3,000 billions of pounds of carbon, or more eharcoal than is contained in the whole of the vegetable and animal kingdoms, and in all the coal deposits below the surface of the earth. Dr. Odling closed his lecture by describing how it was proved by experiment over and over again, that the leaves of growing plants absorb carbonic acid gas from the atmo sphere, and appropriate the carbon contained therein. It is, therefore, demonstrated that most of the carbon helping to form trees, plants, grass, and corn comes from the atmosphere, and not from Mother Earth.