Natural History.

— Baron Humboldt, in a memoir read to the Institute19th February last, entitled, “New Observations on the Laws which weobserve in the Distribution of Vegetable Forms,” states, that we already knownearly 56,000 species of cryptogamous and phanerogamous plants, 44,000insects, 2,500 fishes, 700 reptiles, 4000 birds, and 500 species of mammi-feræ. In Europe alone, according to the researches of M. Humboldt andM. Valenciennes, there exist nearly 80 mammiferæ, 400 birds, and 30reptiles. There are, of consequence, under this temperate boreal zone, 5times as many species of birds as of mammiferæ; as, in like manner, thereare in Europe 5 times as many compositæ as amentaceous and coniferousplants; 5 times as many leguminous as there are of orchideous and euphor-biaceous. The fine collections recently brought home from the Cape ofGood Hope by M. Delalande prove, (if we compare them with the works ofM. M. Temmink and Lavaillant,) that in that part of the temperate australzone, the mammiferæ are also to the birds in the proportion of 1 to 4.3.Such an accordance between two opposite zones is very striking. Thebirds, and especially the reptiles, increase much more towards the equato-rial zone than the mammiferæ. According to the discoveries of M. Cuvieron fossil bones, we might believe, that these proportions have not been thesame at all times; and that there have disappeared, in the ancient cata-strophes of our planet, many more mammiferæ than birds. We can con-ceive how, on a given space of territory, the individuals belonging todifferent tribes of plants and animals may be numerically limited; how,after an obstinate struggle and long oscillations, a state of equilibriumcomes to be established, resulting from the necessities of nourishment andthe habits of life: but the causes which have limited the forms are hid underan impenetrable veil, which withdraws from our view whatever relates to theorigin of things, or to the first developement of organic life.

On the preponderance of certain families of plants depends the characterof the landscape; the aspect of a smiling or majestic nature. Theabundance of gramineæ which form vast savannahs, that of palms and coni-feræ, have had a powerful influence on the social condition of nations, ontheir 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.