their area much further northward, I must remind you, that such is far from being a type of the vegetation of the zone under consideration, either on the Asiatic or North American continents, for as barley generally comes to maturity as far north as 70 degrees in the one, yet, at a similar latitude in the other two the ice-bound earth yields but a few inches depth of soil, capable of supporting only the scantiest vegetation. Along the north of Europe the spruce appears to take the place of the Scotch fir, and with it are associated the birch, the alder, and several species of poplar and willow, though rarely do even these acquire the true arborescent character. But as we find the higher forms of organic life diminish, we also find that the lower classes, such as the lichens and mosses, become more numerous, and not only more numerous, but that they rise to a position of the utmost importance in the maintenance of animal life, as, for instance, the Iceland and reindeer mosses, both abounding in nutritious and mucilaginous properties. What a bounteous provision is not this of an all-wise Providence, that, even these inhospitable regions, present in such abundance one of the greatest essentials to the existence of man and the herbivorous animals, and that, too, from a class of plants, which in our more favoured clime, is deemed scarcely worth a passing glance.

We now come to the last, or polar region, which includes all the terra firma lying within the 72nd parallel of latitude, totally devoid of trees or even shrubs, if we except a few trailing willows, which show signs of vitality for but two short months of the year, and have to contend with a mean annual temperature far below the freezing point. This zone can offer little either to attract or interest an ordinary observer, nevertheless, the botanist will there meet with large social patches of the rare alpine plants, diminutive in stature, 'tis true, but none the less beautiful; and doubtless, by one whose lot is cast in that inhospitable region, their annual re-appearance must be looked forward to with more intense anticipa

tions, and realise a greater amount of pleasure than can be experienced from the same source in any other region of the earth. This polar zone bears an exact correspondence to the alpine region of the mountains, or that occuring immediately below the line of perpetual snow. It matters not what parallel of latitude the mountains are in,—whether in Java, beneath the equator, the Himalayas, the Alps, or the highest of the British mountains--though they be isolated thousands of miles from each other, yet some species of these Alpine plants are common to all, thereby giving to the mountain tops the character of islands in a vast aerial ocean, displaying the same peculiarities of vegetable life. There is a striking similarity between the zones or belts of vegetation which encircle our mountains and those I have described. Any person who has enjoyed a ramble in the highlands of Scotland,-where the hills attain a considerable height, and where the Scotch fir owes not its localisation to the hand of man, must have observed, as he ascended, that the forms of vegetation underwent a change: from the trees which characterise our lowland scenery, we emerge into woods of the Scotch fir; these are followed by dwarf juniper and myrtle berries, and numerous species of sedge grass; approaching nearer their summit, the interesting and appropriately named "Alpine" plants, remarkable for their diminutive size and disproportionately large flowers, discover themselves on every side. If this character is so marked as to attract the attention of the general observer on the insignificant mountains of our island home, how much more striking must it be on the Alps, the Himalayas, or the Andes, whose eternally snow-crowned summits glitter and sparkle in the thin atmosphere high above the region of the clouds?

No

mountain, perhaps, offers so good an example as that selected by Humboldt for his illustration, namely, the Peak of Teneriffe, which rises from the sea level, in a regular and gigantic cone, to the height of 12,000 feet,

and has many advantages from its isolated position, for being surrounded by a wide expanse of water, it enjoys on all sides an equal degree of temperature and humidity, causing the divisional lines of the various regions to be more horizontal and regular than are to be met with elsewhere.

The line of perpetual snow is affected and modified, in a similar manner to the surface distribution of vegetation, by the deflection of the lines of heat and cold. On Chimborazo, situated almost beneath the equator, the snow line is, according to Humboldt, between 15,000 and 16,000 feet above the level of the sea; whereas, fifteen degrees further south, on the Cordilleras, the snow line is at an altitude of 17,000 feet. How can we account for this seeming anomaly? Chimborazo rises from a range whose base is little elevated above the sea level, whereas the Cordilleras of South Peru assume their real mountain altitude from the surface of a vast plateau elevated some thousands of feet; the heat radiating surface of the earth being thereby so much higher affects the atmosphere to a proportionately higher altitude. In addition to this, the plateau on the east side of the range is remarkable for its aridity and bareness of vegetation, the former peculiarity rendering its surface a great absorber of heat, the latter offering little or no hindrance to its direct radiation.

The division of the mountain Flora into various regions or altitudinal zones, is more distinctly marked than the zones of the earth; at least, in the condensed form which we there find vegetation, we are enabled to appreciate them by the direct powers of the visual organs much more so than those of the entire earth's surface, which must of course be viewed through the indirect and uncertain agency of the mind's eye.

To illustrate this division of my subject, imagine three mountains; the first one situated on the equatorial zone, presents the full compliment of eight distinct

regions, each limited to about 1,900 feet of altitude. The second, as for example Mont Blanc, rising from the warmer temperature, presents only five; and the third, from its position in the arctic zone, has but two regions. From this you will observe that the vegetation of a mountain, if of sufficient height, represents the vegetation of the latitudinal zone in which it is placed, and all the others which occur between it and the polar limit.

Was the distribution of plants a feature of the creation itself, or is it attributable, as is more generally supposed, to a dissemination from one, or from many centres? Let us imagine it to have proceeded from one centre, then we should naturally expect that similar circumstances of soil and climate would present a great number of species in common, and that the distribution would be much more than it really is; but the main objection centres itself in the difficulty we experience in accounting for the process of this distribution by any means, mechanical or otherwise, that we know of at the present day.

Certainly the sperules of the lower forms, such as the ferns, mosses, and fungi, may, and I would not hesitate to say, do, imperceptibly impregnate the whole atmosphere, and doubtless can thus be distributed to any extent. Many kinds of seeds also have peculiar feathery appendages beautifully adapted as wings, to assist in their migration, a familiar instance of which we have in the dandelion; but granting these appendages, and the power of the ærial currents as well as the oceanic,the importance of the latter, by the way, recent experiments made to ascertain the length of time seeds will retain their vitality when immersed in salt water, prove to have been much overrated, I say, granting all these mechanical means of diffusion, though they doubtless have a locally distributive influence, I do not think they are sufficient to account for the transmission of seeds or plants across so wide an expanse of water as is presented by the Atlantic or Pacific oceans.

If these currents had the power attributed to them by some, why do our islands lying within the influence of the Gulf stream, not present characteristics of the American Flora? The astered and solidagineœe, which constitute a large and important feature in the American vegetation, have each of their seeds supplied with a feathery crown similar to our dandelion, and yet we have no instance of a single species being transported to our islands. Perhaps the most conclusive evidence against the hypothesis is to be found in those islands which are far distant from any continent, such as St. Helena, Juan Fernandez, and the Galapagos Group; for in each of these we find species and genera which are endemic, or peculiar to that island, and not occuring elsewhere.

In considering this subject I am inclined to think that too much importance is given to the phenomena of our globe, in its present quiescent state. We are

thereby liable to be misled when we consider such phenomena as the only media by which to account for the distribution of vegetation. Were we to go a little further back, and call in to our assistauce the arcana of the past, which are entombed in the earth's bosom; were we to consult carefully those stratified pages of the geological history of our planet, we might look with much greater probability for the solution of our difficulty.

In those pages we should find that each succeeding epoch added to the animal kingdom a higher state of development, and a more complicated organisation. We know that vegetation of some kind is absolutely essential to the support of animal life, and must in the order of creation have preceded it. Are we not justified by direct analogy in drawing the inference that each epoch developed also in the vegetable covering of our earth a higher organisation? And as proof of this, do not those same geological pages present the distinctly outlined fronds of the ferns-stems of giant lycapodes associated