The intimate organic structure of the vegetable world is seen to consist of a variety of different materials indeterminable by unassisted vision, and for the most part requiring high magnification for their discrimination. Chemical analysis had, however, shown that vegetables are composed of a few simple substances, water, carbonic acid gas, oxygen, nitric acid, and a small portion of inorganic salts. Out of these simple elements the whole of the immense variety of substances produced by the vegetable kingdom are constructed. No part of the plant contains fewer than three of these universally distributed elements, hence the greater uniformity in their chemical constituents. It will be seen, then, that the methods of plant chemistry are of supreme interest both to the chemist and the physiologist, or biologist. Plants, while they borrow materials from the inorganic, and powers from the physical world, whereby they are enabled to pass through the several stages of germination, growth, and reproduction, could not accomplish these transformations without the all-important aid of light and heat, the combined functions of which are indispensable to the perfect development of the vegetable world. Light, then, enables plants to decompose, change into living matter, and consolidate, the inorganic elements of carbonic acid gas, water, and ammonia, which are absorbed by the leaves and roots from the atmosphere and earth; the quantity of carbon consolidated being exactly in proportion to the intensity of the light. Nevertheless, light in its chemical character is a deoxidising agent, by which the numerous neutral compounds common to vegetables are formed. It is the principal agent in preparing the food of plants, and it is during the chemical changes spoken of that the specific heat of plants is slowly evolved, which, though generally feeble, is sometimes very sensibly evolved, especially so when flowers and fruits are forming, on account of the increase of chemical energy at this period. The action of heat is measurable throughout the whole course of vegetable life, although its manifestations take on various forms--those suited to the period and circumstances of growth. Upon the heat generated depends the formation of protein and nitrogenous substances, which abound more directly in the seed buds, the points of the roots, and in all those organs of plants which are in the greatest state of activity. The whole chemistry of plant life, in fact, is manifest in this production of energy for drawing material from its surroundings; therefore the organising power of plants bears a direct ratio to the amount of light and heat acting upon them.