All plants are produced from seeds or buds - the one free, the other attached; the one spreading the plant geographically, the other increasing its individual size. Carefully examined, the seed, or starting-point in the life of a plant, is composed of a leaf rolled tight, and altered in tissue and contents so as to suit its new requirements. Look at the germination of a Bean: the two leaves of which it is composed appear in the fleshy lobes or cotyledons which first rise above the ground, and afford nourishment to the embryo. The bud, which is physiologically co-ordinate with the seed, is found to consist of leaves folded in a peculiar manner, and covered with tough leathery scales to protect them from the winter's cold; and in spring it evolves the stem, leaves, and fruit. By some the stem is regarded as an essentially distinct and typical part, but the study of plants in which it departs from the normal form will clearly indicate its foliaceous origin. The leaf is here made to assume a columnar shape, strengthened at the joints and nodes for the support of the superstructure, and elevated above the ground in order to expose all the organs which it bears to the quickening influence of sun and air.

In plants which are destitute of ordinary leaves, or which shed them at an early period, and remain ever after naked, the stems serve all the purposes of leaves. In the Cactus tribe, the whole plant consists of pointed leaves, and in the common Butcher's Broom of our own country, the stem becomes foliaceous - that is, flattened and leaf-like. Stems produce buds and flowers, so do leaves - as, for instance, those of the Bryophyllum. Indeed, every leaf is a modified branch, and its toothed or serrated edges correspond with the nodes of the stem.

Further, all the appendages borne on the stem - such as scales, leaves, bracts, flowers, and fruit - are modifications of this one common type. Flowers, the glory of the vegetable world, are merely leaves, arranged so as to protect the vital organs within them, and coloured so as to attract insects to scatter the fertilising pollen, and to reflect and absorb the light and heat of the sun for ripening the seed. Stamens and pistils may be converted, by the skill of the gardener, into petals, and the blossoms so produced are called double - necessarily barren. The Wild Rose has only a single corolla. Cultivated in rich soil, its yellow stamens are changed into the blush leaves of the full-blown Cabbage-Rose. There is a monstrosity to which the Garden Rose is liable - the stamens and pistils are converted into green leaves, and the plant begins to develop stem and foliage from the bosom of the petals, just as though the blossom were not the culminating point, but merely a stage in its growth. We see the whole gradual process in the metamorphosis of the common leaf into all the floral organs most beautifully displayed in the normal flower of the common Water-Lily - the outermost circle of petals is greenish, approaching the herbaceous texture and colour of the calyx; the next circles are purer and more succulent; and the innermost ones are snowy white, entirely cellular, and, strange to say, begin to show rudiments of an anther at their points.

Gradually the petals become smaller and narrower, while the anthers on their summits become more distinct, until at length the usual thread-like filaments and golden dusty anthers of perfect stamens appear in the heart of the flower.

We come next to the fruit, which, in all its astonishing varieties of texture, colour, and shape, is also a modified leaf; and it is one of the most interesting studies in natural history to trace the correspondence between the different parts of structures so greatly altered and the original type. In the Peach, for instance, the stone is the upper skin of a leaf hardened so as to protect the kernel or seed; the pulp is the cellular tissue of a leaf expanded and endowed with nutritive properties for the sustenance of the embryo plant; and the beautiful downy skin on the outside is the lower cuticle of the leaf, with the sun-bloom upon it, the hollow line on one side of the fruit marking the union between the two edges of the leaf. So also in the Apple - the parchment-like cover is the upper surface of the leaf, and the flesh is the cellular tissue greatly swollen. In the Orange, the juicy lips enclosing the seeds are the different sections of the leaf developed in an extraordinary manner; while through the transparent skin of the ripe Gooseberry we see the ramifications of the leaf-veins, conclusively proving its origin.

In all the parts and organs of the plant, then, from the seed to the fruit, we have found that the leaf is the type and pattern after which they have been constructed, and those modifications of structure, colour, and composition which they exhibit are for special purposes in the economy of the plant in the first place, also for services to the animal creation, and even to man himself, to whom the sweetness of the fruit and the beauty of the flowers must have had reference in the gracious intention of Him who created them both.

D. Hugh Macmillan.