simple aggregation of cells, as in the sea-weeds and lichens, to the more complex fronds of the ferns and club-mosses; from these to the parallel-nerved leaves of the grasses and palms; and from these again to the reticulated and more highly organised venation of the leaves of the flowering shrubs and true timber-trees. He further finds that, while the leaf is produced by the development of the cell, all the other organs of the plant are but modifications of the leaf -that the stem and branches are elaborated from the successive growths of leaves, that the petals of the flower are but modifications of the same organ for a special purpose, that the fruit is but a specialised combination of leaves, and that the seed itself consists of a leaf or leaves folded up and protected for the return of those conditions of heat and moisture necessary to its starting again into life and verdure, to perform the same round of development and reproduction. How this cell, or globule of matter, should become vivified-how it should be capable, under certain conditions of heat, light, and moisture, of being reproduced indefinitely into some determinate form as a leaf, and how these leaves or leaf-like organs should be persistently maintained, each in its own distinctive type throughout the great categories of the vegetable kingdom-are problems which science cannot solve. We know, however, the facts and the order of their occurrence. We perceive the expression of a prescient plan; that plan we endeavour to interpret. Everywhere purpose and design are manifest; into the motives of the Designer we may not inquire. The secondary we may discover: to the primary we can only appeal.

Founding on this great principle of cell and leaf development, the botanist traces its elaboration in the different races of plants, and regards those which manifest little more than a repetition of the same parts as of lower organisation

than those in which the leaf is metamorphosed into various organs, each organ having a special function to perform in the plant's growth and perfection. The higher, therefore, that a plant is in the scale of being, the more specialised its organisation; that is, instead of all the functions or several of its functions being performed by the same organ, each function is performed by an organ specially devoted to it. It is thus that the fern is regarded higher than the seaweed; the palm higher than the fern; and the oak than the palm. In ranking plants as "higher" and "lower," the botanist by no means asserts that the one is less fitted than the other for its purpose in creation. All that he affirms-and common-sense homologates the affirmation— is, that the lichen, composed of a mere congeries of cells, and increasing by a mere homogeneous development of these cells, is a less highly organised structure than the timber-tree, in which is elaborated a variety of tissues, which is increased by leaf-growth, and whose reproduction is provided for by a complicated process of flowering and fructification. Aware of these distinctions, and knowing the persistency of nature in her modes of operation, we can determine the relative positions not merely of the plants that now adorn the various regions of the earth, but of those that existed during the successive epochs of her bygone history. As a region of shrubs and timber-trees is said to enjoy a higher flora than a region of ferns and clubmosses, so do the reticulated leaves and concentric woody layers, found fossil in a recent rock-system, give indication of a higher physiological value than the parallel-veined leaves and vascular-bundled stems of some earlier formation. It is thus that we arrive, in general terms, at the great truths of vital progress—a leaf, a stem, the disposition of a branch, or the structure of a fruit, affording such evidence to the palæontologist as the flint arrow-head, the

bronze spear, and the primitive matchlock, afford to the archæologist and historian.

Proceeding upon such principles as those indicated in the preceding paragraphs, the botanist arranges all vegetables into two grand divisions-the CELLULAR and the VASCULAR: the former embracing those which, like the mushrooms and lichens and sea-weeds, possess no regular vessels, but are composed of a mere congeries of cells or cellular tissue; the latter comprising those that are composed of various tissues and furnished with various organs of nutrition and reproduction. Again, he subdivides the vascular into the FLOWERLESS, as the mosses, equisetums, and ferns; and the FLOWERING, which embraces the palms, and lilies, and grasses, the pines and cycads, and all herbs and shrubs, and true timber-trees. In the Flowerless division (Cryptogams or Sporocarps, as they are sometimes termed) the organs of reproduction are not essentially different from the other parts; that is, they are not apparent-similar cells forming alike the organs of growth and the organs of reproduction. On the other hand, in the Flowering (Phanerogams or Spermocarps) the organs of reproduction are apparent the seed being enclosed in an embryo in which the rudiments of the future plant are distinguishable. Still subdividing and arranging, he speaks of Dicotyledons, or those whose seeds, like the bean and acorn, are furnished with two lobes; of Monocotyledons, or those like the palms and grasses, which have only one seed-lobe; of Acoty-. ledons, or those like the ferns and fungi, which have no lobes, but are propagated by spores, and so termed Sporocarps in contradistinction to the Spermocarps, or those bearing true seed-fruits. Again, looking at their modes of development, the botanist speaks of Exogens, or plants whose stems increase by external layers of annual growth around a central pith-hence the concentric rings of the ash and beech;

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of Endogens, whose increase takes place from within by a coalescence of the footstalks of the old leaves, as in the palm; of Acrogens, or those that increase by shooting from the top, as the ferns and horsetails, and whose stems are thus generally thicker above than below; and of Amphigens, or those which grow by additions to the external margin, and spread, as it were, on every side, as in the sea-weeds and lichens. Founding in this way-first, on the different modes of reproduction; second, on the aspect of the reproducing organs; thirdly, on the primary development; and fourthly, on the ultimate development of the plant-the botanist arrives at a scheme of classification which may be briefly expressed as in the annexed tabulation.

It is true, the palæontologist cannot always avail himself of the terms and classification of the botanist, as there occur in the geological formations a number of forms that stand intermediate between existing orders and families, and of which we have now no living representatives. Still, these forms never diverge so widely from any of the existing families but that their affinities can be determined with some degree of certainty; and at all events, even where family alliance fails, they can be readily ranked under the wider categories of orders and sections. It is thus that the subjoined scheme embraces alike the extant and extinctthe latter supplying the links that unite the whole into a still more homogeneous and consistent system: