For the perfect understanding of the physical conditions under which vegetable life is carried on, it is necessary to appreciate, in its fullness, the value of the term _growth_. It has been said that stones grow—that the formation of crystals was an analogous process to the formation of a leaf; and this impression has appeared to be somewhat confirmed by witnessing the variety of arborescent forms into which solidifying waters pass, when the external cold spreads it as ice over our window-panes. This is, however, a great error; stones do not grow—there is no analogy even between the formation of a crystal and the growth of a leaf. All inorganic masses increase in size only by the accretion of particles—layer upon layer, without any chemical change taking place as an essentiality. The sun may shine for ages upon a stone without quickening it into life, changing its constitution, or adding to its mass. Organic matter consists of arrangements of cells or sacs, and the increase in size is due to the absorption of gaseous matter, through the fine tissue of which they are composed. The gas—a compound of carbon and oxygen—is decomposed by the excitement induced by light; and the solid matter thus obtained is employed in building a new cell—or producing actual growth, a true function of _life_, in all the processes of which matter is constantly undergoing chemical change. The simplest developments of vegetable life are the formation of confervæ upon water, and of lichens upon the surface of the rock. In chemical constitution, these present no very remarkable differences from the cultivated flower which adorns our garden, or the tree which has risen in its pride amidst the changing seasons of many centuries. Each alike have derived their solid constituents from the atmosphere, and the chemical changes in all are equally dependent upon the powers which have their mysterious origin in the great centre of our planetary system. Without dwelling upon the processes which take place in the lower forms of vegetable life, the purposes of this essay will be fully answered by taking an example from amongst the higher class of plants and examining its conditions, from the germination of the seed to the full development of the flower—rich in form, color, and odor.