The British Isles are estimated to contain 110,181 square miles, and their total vegetation, omitting algae and fungi, is composed of 2,393 species, or one to every 46 square miles. These are distributed among 939 genera and 112 families. The value of the genus, or its average proportion of species, is 37; of the family, or its proportion of genera, is 5'7; of the exogenous genus, 2.8; of the same family, 47; of the endogenous genus, 28; of the same family, 67; of the cryptogamic genus, 85: of the same family, 13. The flora has little to distinguish it from the continent of Europe.

Ireland has 682 exogenæ, 211 endogenæ, and 41 ferns. Some plants are found there not indigenous to Great Britain, but generally occurring to the south of Europe; as, arbutus unedo, menziesia polifolia, papaver nudicaule, sedum palustre, arenaria ciliata, saxifraga umbrosa, pinguicula grandiflora, trichomanes brevisetum, hookeria lætevirens, and h. splanchnoides. The two last are quite peculiar.

RELATIONS.-Besides the close relations to neighbouring regions, some interesting affinities exist with the distant Patagonia and Van Diemen's Land Regions. Compared with its American parallel, the Iroquois Region, it fails greatly in variety, and particularly in the forest

trees.

XLVII. THE VOLGA REGION.

EXTENT.-Russia, to the west of the Ural Mountains, and to the north of a line commencing at the fifty-fifth degree of latitude on the Baltic, and extending to the Sea of Azof; with the whole of Norway and Sweden, with

the exception of a small portion of their southern ex

tremes.

PHYSICAL CHARACTERS.- Russia consists chiefly of an extensive plain of inconsiderable elevation, and dotted with numerous lakes and marshes, and Norway and Sweden are intersected by lofty mountains.

CLIMATE. To the eastward the climate is one of extremes, the summers being hot and the winters long and severe. On some days the temperature is higher than is usual many degrees to the south. The western countries have a more even climate, but still a rigorous one.

FLORA. The extensive and often magnificent forest, which covers nearly the whole of this region, is composed chiefly of pinus sylvestris, mingled with abies picea, and a. communis; and pinus cembra is met with towards the Ural Mountains. Though the species of pine are fewer here than in the south, the trees are of far finer growth; a circumstance that occurs also with the eucalyptus in Van Diemen's Land, where, though there are fewer species, the trees grow much larger. Sheltered by the forest, a dense undergrowth flourishes, of species of vaccinium, andromeda, empetrum, rubus, salix, betula, and arctostaphylos. Conifera, amentaceæ, saxifrageæ, cruciferæ, and ranunculaceae, are particularly prominent, and some members of umbelliferæ, caryophylleæ, and boragineæ, are mixed with the vegetation, but are rapidly disappearing. An English botanist visiting this region will find most of the northern plants of his own island, but will perhaps be more surprised to see what an altered character a vegetation of similar species assumes here; for he will find many plants very common, which were rare at home, and others before regarded as common weeds are here prized. Senecio jocobæa, so frequent a nuisance in our meadows, is in Norway an object of diligent search. Several important plants have their northern limits in

this region. Quercus robur ceases at 61o, fraxinus excelsior 60o, fagus sylvatica 60°, prunus cerasus 57°-60°, tilia intermedia 63o, abies communis 67°, populus alba and p. nigra 56o, pinus sylvestris 70°; the ash, alder, aspen, and juniper, in Norway, reach the arctic circle, or 67o, but cease near the Urals at 60o.

Alpine vegetation can scarcely be supposed to exist in a region which possesses so many of its characters, and any attempts to give it prominence will be attended with very feeble results. In Lapland, between 66° and 68°, according to the statements of Wahlenberg, the Region of Trees attains 1,800 feet; the Region of Shrubs succeeds to 2,500 feet, and is closed in by lichens and perpetual snow at 3,300 feet. In Finmark, according to Von Buch, at 70o, pinus sylvestris grows to 730 feet; betula, larix, and vaccinium, to 3,100 feet; then cryptogamic vegetation and perpetual snow at 3,300 feet.

RELATIONS. The parallel regions in America are filled with forests of noble trees of abies instead of pinus, mixed with cupressus thyoides, and occasionally a pine, cratægus, or fraxinus; besides this there is much similarity in the vegetation.

XLVIII. THE OCEAN REGION.

EXTENT. The shores and shoal waters of the ocean through all latitudes, from high-water mark to a depth at present uncertain, but which most probably is inconsiderable.

PHYSICAL CHARACTERS.-The medium in which marine plants live may, in several ways, affect the functions of those which select it for their habitation. The influence of the atmosphere is nearly excluded; and light, even at

small depths, is greatly obstructed. The saline constituents must be regarded as essential to their well being, though I have seen a fucus and a potamogeton growing together in water of a very slight degree of saltness. In many cases they evidently display a selection as to their place of attachment, and usually prefer mud or soft rocks to harder substances. They appear particularly scarce in coral islands, perhaps because the coral animal feeds on them.

CLIMATE. The seasons and temperature have a decided influence. In the summer months this flora is in great vigour, and when a season occurs eminently favourable to vegetation, it is proportionately affected. From their geographical distribution it may be inferred that these plants are sensible of small variations in the habitual temperature. Within the tropics those living in shoal waters are surrounded by a temperature varying from 74o to 86°. At greater depths the temperature gradually and evenly descends. A decrease, however, does not always happen. In 25° N. lat., when the air was 67° and the surface of the sea 69°, the temperature at 35 feet was 73°. The temperature at the surface will generally be found to fluctuate about the mean of the latitude, but is liable to be disturbed by currents, as is the case with the gulf stream, which so modifies and warms the climate of the Bermudas. In high latitudes the surface may be sometimes below the mean temperature, and an increase occur for certain depths, but this will rarely exceed 42° or 44°.

FLORA.-Notwithstanding the uniformity of the ocean, the facilities of diffusion, and simple organization of the vegetable beings which inhabit it, they will be found often remarkably circumscribed in their limits of growth. The same laws prevail as on the land, that there shall be everywhere variety, and that under similar circumstances in widely separated localities there shall be close relations.

Looking over, then, this extensive region, the different deep inlets, gulfs, and seas, will each be found to have their own peculiar kinds, and sometimes in such numbers as almost to justify their exaltation into separate regions. It is said that the species found in the Red Sea are almost entirely different from those of the coast of Syria, though separated by so small a portion of land. In our own island rhodomenia cristata and odonthalia dentata are confined to the northern shores; and fucus tuberculatus, laurencia tenuissima, rhodomenia jubata, rhodomela pinastroides, iridæa ensiformis, and others, to the southern.

The flora of this region is entirely derived from the natural family of algæ, but does not comprehend all its species, since many prefer fresh waters. Lamouroux has calculated that the total number of species may reach 5,000, or even 6,000. Fucus and laminaria exist in enormous beds in the high latitudes of both hemispheres. Several species of sargassum replace the former within the tropics, where they are often densely crowded on the surface, and generally in an active state of vegetation. Tamnophera, caulerpa, gelidium, amansia, and dictyoteæ are chiefly tropical. Codium tomentosum is found in nearly all seas throughout the world. Macrocystis belongs to the southern hemisphere from the equator to 45° S. lat, and durvillea and lessonia are likewise limited to this part of the world. Thaumasia ovalis, a remarkable plant, is found only at Ceylon. Cystoseira has several species on our own coasts, and others abound in the northern hemisphere, but a peculiar group is met with in New Holland, where, Greville remarks, it is as peculiar as the aphyllous acacia are on the land.

RELATIONS.-Between the terrestrial and marine vegetation the link is perfect and complete. Of the latter, the mass unquestionably find the waters of the ocean essential