Vegetable forms of a higher and a higher order gradually succeed each other, each series perishing in due season, and giving to the soil additional elements for the growth of plants of their own species or those of others. Flowering herbs find a genial home on the once bare rock; and the primrose pale, the purple foxglove, or the gaudy poppy, open their flowers to the joy of light. The shrub, with its hardy roots interlaced through the soil, and binding the very stones, grows rich in its bright greenery. Eventually the tree springs from the soil, and where once the tempest beat on the bare cold rock, is now the lordly and branching monarch of the forest, with its thousand leaves, affording shelter from the storm for bird and beast. Such are the conditions which prevail throughout nature in the progress of vegetable growth; the green matter gathering on a pond, the mildew accumulating on a shaded wall, being the commencement of a process which is to end in the development of the giant trees of the forest, and the beautifully tinted flower of nature’s most chosen spot. We must now consider closely the phenomena connected with the growth of an individual plant, which will illustrate the operation of physical influences throughout the vegetable world. The process by which the embryo, secured in the seed, is developed, is our first inquiry. A seed is a highly carbonized body, consisting of integuments and embryo: between these, in most seeds, lies a substance called the _albumen_, or _perisperm_. The embryo contains the elements of the future plant--the cotyledons, the plumule, and the radicle; the former developing into stalk and leaves, the latter into roots. This embryo hides the living principle, for the development of which it is necessary that the starch and gluten undergo a chemical change, and that an elevation of temperature is produced. The vital power is dormant--it sleeps--in the seed until the proper conditions are produced. It has been proved, that the powers of maintaining life in the seed are very great; excessive cold, sufficiently intense to freeze mercury, will not kill seed, and they resist a comparatively high temperature. It is probable that heat only destroys seeds by drying them too completely. The temperature at which seeds germinate is exceedingly varied,--those belonging to our own clime will germinate when the thermometer rises above 40° F., but the seeds of tropical plants demand that a temperature of from 70° to 84°, or even to 90°, be steadily applied to them. In some cases it has been found that even boiling the seeds has been advantageous to the future process of germination in the soil. But let us take the seed of some ordinary plant, and trace its progress.