“In consequence of a flower and its peduncle being a branch in a particular state, the rudimentary or metamorphosed leaves which constitute bracteæ, floral envelopes, and sexes, are subject to exactly the same laws of arrangement as regularly-formed leaves.”[257] The idea that the leaf is the principal organ of the plant, and that from it all the other organs are probably developed, is worthy the genius of the great German poet. Every leaf, a mystery in itself, is an individual gifted with peculiar powers; they congregate in families, and each one ministers to the formation of the branch on which it hangs, and to the main trunk of the tree of which it is a member. The tree represents a world, every part exhibiting a mutual dependence. “The one red leaf, the last of its clan, That dances as often as dance it can; Hanging so light and hanging so high, On the topmost twig that looks up at the sky,” is influenced by, and influences, the lowest root which pierces the humid soil. Like whispering voices, the trembling leaves sing rejoicingly in the breeze and summer sunshine, and they tremble alike with agony when the equinoctial gale rends them from the parent stalk. The influences which pervade the whole, making up the sum of vital force, are disturbed by every movement throughout the system; a wound on a leaf is known to disturb the whole, and an injury inflicted on the trunk interferes with the processes which are the functions of every individual leaf.[258] The consideration of the physical circumstances necessary to germination and vegetable growth, brings us acquainted with many remarkable facts. At a temperature below the freezing point, seeds will not germinate; at the boiling point of water, a chemical change is produced in the grain, and its power of germinating is destroyed. Heat, therefore, is necessary to the development of the embryo, but its power must only be exerted within certain prescribed limits: these limits are only constant for the same class of seeds, they vary with almost every plant. This is apparent to every one, in the different periods required for germination by the seeds of dissimilar vegetables. The seed is placed in the soil; shade is always--absolute darkness sometimes--necessary for the success of the germinating process. We have seen that the first operation of nature is purely a chemical one, but this manifestation of affinity is due to an exertion of force, which is directly dependent upon solar power. The seed is buried in the soil, when the genial showers of spring, and the increasing temperature of the earth, furnish the required conditions for this chemistry of life, and the plant eventually springs into sunshine. Thus we obtain evidence that even through some depth of soil the solar power, whatever it may be, is efficient, and that under its excitement the first spring of life, in the germ, is effected.