RELATIONS.-Between the tropical portions of Asia, Africa, and America, many of the natural families are shared in common; thus we see combretaceæ, meliaceæ, ochnaceæ, sapindaceæ, terebintaceæ, anonaceæ, sapoteæ, and potaliaceæ, all essentially tropical groups, freely represented in each. Frequently the genera are in common, but beyond this the relations are feeble. Still some extensive families are only sparingly represented, as passifloreæ, melastomaceæ, myrtaceæ, and loranthaceæ. It is probable that when the vegetation of the base and flanks of the Cameroon Mountains shall be known, they will require a separate consideration. Their supposed elevation is 13,000 feet.

XXIX. THE CANARY ISLANDS REGION.

EXTENT. These islands are in the same parallel at the Great Sahara, being situated off that part of the African coast where that desert meets the ocean, and are thus situated, in a geographical position, between the Barbary Region and the West Africa Region. In addition to the islands more properly known as the Canaries, the region includes the fertile island of Madeira, with the almost desert Porto Santo and the Dezertos, and the Azores.

PHYSICAL CHARACTERS.-The islands of these groups may be regarded as so many mountains rising above the ocean to considerable elevations. Teneriffe attains 12,176 feet, and the highest part of Madeira, 6,233 feet. Their plains and valleys abound in a fertile soil, the productiveness of which is further insured by its volcanic origin, insular position, copious supply of moisture, and warm atmosphere. In some parts lava prevails so completely as to exclude vege

tation, and those islands with an aspect towards the coast of Africa are materially affected by its arid breezes.

CLIMATE. The temperature is warm and even, but some parts are subject to considerable depression from sudden gusts, which sweep the cold air from the summits. The mean of Funchal, Madeira, is 65°, number of rainy days 73, and fall of rain 31 inches. At Santa Cruz, Teneriffe, the mean is 71°. The temperature given for the alpine regions of vegetation are calculated; those used by Spix and Von Martius are assumed from the calculations of Howard; we therefore pass them over till we possess strictly observed data.

FLORA. This must be regarded as an alpine region, and the different portions of its flora have been described by Humboldt, Von Buck, Von Martius, and Kuhl. There is, however, some discrepancy between their statements; for not only are the alpine regions of Teneriffe made to differ from those of Madeira, but also from the rest of the Canaries. In attempting to reduce them to mutual consistency we shall follow out the views we have previously expressed on this subject.*

Teneriffe has been ably examined by Humboldt, and his regions are nearly natural.

1. The Region of Lowland Cultivation extends to 1,800 feet. It is distinguished by the presence of a few tropical forms; dracæna draco, phoenix dactylifera, chamaerops humilis, musa paradisaica, m. sapientum, arborescent euphorbias, and some species of mesembryanthemum from Africa, meet species of cactus from America.

2. The Region of the Woods extends to 7,200 feet. These woods are lofty and extensive, and comprise laurus indica, 1. fœtens, 1. nobilis, rhamnus glandulosa, erica

*London Journal of Botany for March, 1842.

arborea, erica texo, quercus canariensis. Ferns are numerous. A convenient subdivision may be established, since the pines occupy only the upper part of this region for the breadth of 25,000 feet; thus constituting-1, the subregion of laurels to 5,400 feet; 2, the sub-region of pines to 7,200 feet.

3. The Region of Shrubs. - Spartium nubigenum abounds, and not much else, for the surface is chiefly volcanic ashes.

4. The Region of Grasses.-Scrophularia glabrata, viola cheiranthifolia, and the cruciferous plants, cheiranthus longifolius, c. frutescens, c. scoparius, erysimum bicorne, crambe strigosa, c. lævigata, are met with.

5. The Region of Cryptogamic Plants.-It contains only urceolaria and other lichens.

Madeira, as the name implies, was formerly covered with woods, but the early cultivation of the sugar-cane, and subsequently of the vine, and still more recently the adoption of grazing, has produced a total change in the original features of the vegetation.

1. The Region of Lowland Cultivation extends to 2,000 feet. The agave, plantain, date, pomegranate, and fig all thrive well. Of sixty species found here, 36 are common to the north of Europe, 17 to southern Europe and northern Africa, and 7 peculiar to the Canary Region. Among them is scarcely a genus with more than one species.

2. The Region of Woods extends to 3,000 feet. The trees are not numerous; castanea vesca, pinus canariensis, laurus fætens, 1. indica, clethra arborea. In thirty-two species, eight only are European, the remainder being peculiar. Here, therefore, the flora is more characteristic, and introduced plants have not attained this elevation.

3. The Region of Shrubs extends to the loftiest part of the island. Spartium scoparium, cytisus divaricatus, erica

scoparia, and vaccinium padifolium, abound. Grasses, belonging to cynosurus, aira, and agrostis, begin to appear on the higher stations.

In Madeira succulent plants are frequent; the trees have coriaceous leaves, and the northern families of amentaceæ, saxifrageæ, and caryophylleæ, are uncommon, as are the tropical families of euphorbiacea and malvaceæ. Of compositæ, the tribe of corymbiferæ is scarce, but cichoracea abundant.

The Azores are situated something to the north of the other islands. Like them they are volcanic, with bold scenery, scarped rocks, deep ravines, and a general elevation of the surface from 2,000 to 5,000 feet. The indigenous flora is scanty, but the climate is good, and highly suited to the growth of tropical and such other fruits as have been introduced. From their supposed comparatively recent origin, the early history and subsequent diffusion of vegetation might be satisfactorily studied here.

RELATIONS.-In such a region a considerable change must have been produced by the extinction of native plants, and the introduction of others. Its affinities are more copious with Europe than south Africa. The species of cactus are regarded as instances of migration from America, and dracæna draco is supposed to have come originally from India. Of 62 plants collected at Teneriffe in Kotzebue's first voyage, 30 were peculiar to our region, 30 common with Europe, and 2 with Africa. Von Buch mentions 533 species as belonging to the Canaries, of which he considers 162 as introduced.

XXX.-THE BARBARY REGION.

EXTENT.-The northern part of Africa, embracing the states of Morocco, Algiers, Tunis, and Tripoli, is separated by the Great Sahara from the rest of the continent, and to the west is beaten by the waves of the Atlantic, whilst to the east it extends nearly to the delta of the Nile. The Atlas range of mountains forms an important portion of this region; and, when better known, will most probably contain its greatest peculiarities. There are also some other mountains of considerable elevation.

PHYSICAL CHARACTERS.-With much dry and barren land, there are also extensive districts of great fertility. The soil is generally sandy, but productive when supplied freely with moisture; and the neighbourhood of the Atlas mountains is indicated as possessing much that is rich and fertile. From the elevated lands numerous streams descend to the plains; those towards the north finding an outlet in the Mediterranean Sea, whilst those falling to the south are chiefly lost in the thirsty sands of the desert. The highest ascertained part of the Atlas range is 11,400 feet, is in the vicinity of Morocco, and clothed with perpetual Salt marshes and lakes, and saline soils, are all of frequent occurrence.

snow.

CLIMATE.-The heat is great, but not so oppressive as in Egypt or Arabia, in the same latitude. At Algiers the mean of the year is 70°, of the summer 80°2, and of the winter 61°4. Vegetation is in its greatest vigiour in autumn, after the rains. It is then that a crowd of herbaceous plants hasten to spread abroad their beauty, retiring rapidly as the moisture disappears; leaving a bushy vegetation to struggle with the parching atmosphere of the dry months.