Baron Humboldt, in a memoir read to the Institute 19th February last, 1821, entitled, "New Observations on the Laws which we observe in the Distribution of Vegetable Forms," states, that we already know nearly 56,000 species of cryptogamous and phanerogamous plants, 44,000 insects, 2,500 fishes, 700 reptiles, 4,000 birds, and 500 species of mammiferae.

In Europe alone, according to the researches of M.

Humboldt and M. Valenciennes, there exist nearly 80 mammiferae, 400 birds, and 30 reptiles.

There are, of consequence, under this temperate boreal zone, 5 times as many species of birds as of mammiferae; as, in like manner, there are in Europe 5 times as many compositae as amentaceous and coniferous plants; 5 times as many leguminous as there are of orchideous and euphorbiaceous.

The fine collections recently brought home from the Cape of Good Hope by M.

Delalande prove, (if we compare them with the works of M. M.

Temmink and Levaillant,) that in that part of the temperate austral zone, the mammiferae are also to the birds in the proportion of 1 to 4.3.

Such an accordance between two opposite zones is very striking.

The birds, and especially the reptiles, increase much more towards the equatorial zone than the mammiferae.

According to the discoveries of M. Cuvier on fossil bones, we might believe, that these proportions have not been the same at all times; and that there have disappeared, in the ancient catastrophes of our planet, many more mammiferae than birds.

We can conceive how, on a given space of territory, the individuals belonging to different tribes of plants and animals may be numerically limited; how, after an obstinate struggle and long oscillations, a state of equilibrium comes to be established, resulting from the necessities of nourishment and the habits of life: but the causes which have limited the forms are hid under an impenetrable veil, which withdraws from our view whatever relates to the origin of things, or to the first developement of organic life.

On the preponderance of certain families of plants depends the character of the landscape; the aspect of a smiling or majestic nature.

The abundance of gramineae which form vast savannahs, that of palms and coniferae, have had a powerful influence on the social conditon of nations, on their manners, and the more or less rapid developement of the useful arts.

Sometimes a single species of plants, especially among those styled, by M. Humboldt, social, covers a vast extent of country.

Such are, in the north, the heaths, and forests of pines; in equinoctial America, the union of cactus, croton, bambusa, and brathys of the same species.--The sequel of this will be given in our next Number.