an extensive range; but, like them, their function is largely physical, and comparatively few of the animal races find subsistence on their stems or foliage. As the peaty marsh, the silty lake, and the shady river-swamp are now their established headquarters, so the increment and consolidation of these by their annual growth and decay has ever been their geological function. Higher than these, and of more varied aspect, come the Gymnogens-the cycads, and yews, and pines-the gregarious forest growths of the present, as of former ages. Lovers of the temperate and coldly temperate zones— s-inhabitants alike of the swamp, the arid plain, and the mountain-they exhibit an enlarged diversity of habit, and form, and function. Like the acrogens, many of them are swamp and coal formers; and, as will be afterwards seen, it is to the acrogens and gymnogens, and especially to extinct intermediate forms, that we are chiefly indebted for the coal-beds of the earlier formations. As foodsuppliers, their function is comparatively limited-their dry rigid foliage, their scaly seeds and fleshless berries, being little fitted for the miscellaneous requirements of the higher animals. And it is a curious coincidence that so few of the higher animals appear in the geological periods where these acrogenous and gymnogenous groups so universally prevail. The Endogens-the grasses, lilies, and palmsfollow next in order, and present a still increasing variety, both in form, habitat, and function. Tropical and temperate, but unfitted for the extremes of climate, they assume more diversified areas of localisation, and become more and more fitted for the sustenance of a varied terrestrial fauna. While radiates, molluscs, and crustacea may feed on the thallogens, and insects, and it may be a few birds and reptiles, find their food and shelter among the acrogens and gymnogens, it is certainly to the endogens and exogens that the higher terrestrial animals turn for their main depend

ence.

The formative or geological function so prominent in the lower groups, now gives place to the alimentative;

and though the grassy carpet may conserve the soil from waste, and the palm-grove may induce the accumulation of vegetable matter, still the relations of the endogens are mainly and obviously zoological. Highest and last come

the Exogens the herbs, and shrubs, and timber-treeswhich, in their beauty and variety and dignity of aspect,

crown the long line of vegetable existences. Slower of growth, but of greater longevity, the beauty of their flowers, the utility of their seeds and fruits, the durability of their structure, and the diversity of their habits and forms, all point to them as the culminating orders of the vegetable

kingdom. And it is curious to learn that, unknown in the earlier eras, and just beginning to make their appearance in the secondary epochs, they come into full force and vigour in the tertiary and post-tertiary-the periods at which the higher animals and man are present to reap the advantages of their more varied utilities.

Such are the leading features of the great groups of the vegetable kingdom-groups to which we shall have frequent occasion to allude when we come to treat the successive stages of the fossil flora, and which are here displayed in pictorial outline with a view to facilitate the comprehension of these allusions. Though thus arranged in physiological groups, the whole, from the simple cell that floats on the putrid pool to the noblest tree of the forest, forms but one orderly and co-adjusted system; and could we combine the extinct with the living, the same order and co-adjustments would be found to run as unswervingly through the wider combination. The conception is one, though its expression through time and space must necessarily assume the character of infinite diversity.

Subdividing still further, according to their most marked characteristics, whether external or internal, the botanist arranges all the forms of vegetable life into some 60 or 70 orders, about 300 genera, and upwards of 100,000 .species. As most of these distinctions, however, are founded on the form and connection of the flower, fruit, and leaf— organs which rarely or never occur in intelligible union and preservation in a fossil state-the palæontologist is guided in the main by the great structural distinctions already adverted to, and not unfrequently by the simple but unsatisfactory test of "general resemblance." On the whole, Fossil Botany, or Palæophytology, as it is sometimes termed, is by no means in a satisfactory state, and the science languishes for the advent of some master minds to do for

it what Cuvier and Agassiz and Owen have done for the sister science of Fossil Zoology.

Notwithstanding the fragmentary state of the plants that turn up to the geologist, the greatly altered conditions of the parts that are found, and the hopelessness of ever discovering the legible dispositions of such evanescent portions as the floral organs, on which so much of existing botany is founded: notwithstanding all these obstructions, there is still so much remaining—the structure of the roots, stems, barks, leaves, fronds, and fruits-the characteristic markings of their different surfaces-and the scars which their parts leave on separation-that the competent botanist, armed with his microscope and ample means of comparison, should have little difficulty in arriving at many definite and important conclusions. The anastomosing disposition of a sea-weed is surely sufficiently distinct from the branching aspect of a terrestrial plant-the reticulate venation of a dicotyledonous leaf from the parallel arrangement of a monocotyledon -the scalariform tissue of a fern from the punctated tissue of a conifer-and the bundled mass of an endogenous stem from the concentric layers of an exogen. These and many other characteristics are sufficiently preserved in the strata of every formation; and though we may not be enabled to say, on the principles of existing botany, that this fragment is that of a cruciferous plant, and that of a leguminous one, we have, at all events, enough to fix in the mean time the great progressional order of plant-life from the predominance of Acrogenous orders in primary formations to the higher Gymnosperms of the secondary, and from these again to the still higher Angiosperms of the tertiary and current epochs. And Geology, strong in the faith of Nature's unity and persistency of plan, rests assured, that under right methods of research the key to that Plan will yet be dis