play—distinguishes between pines or palms and beeches in the background of a landscape, but not between forests of beech and other thickly foliated trees. The physiognomy of nature is principally determined by sixteen forms of plants. I merely enumerate such as I have observed in my travels through the old and new world during many years’ study of the vegetation of different latitudes, between the parallels of 60° north and 12° south. The number of these forms will no doubt be considerably increased by travellers penetrating further into the interior of continents, and discovering new genera of plants. We are still wholly ignorant of the vegetation of the south-east of Asia, the interior of Africa and New Holland, and of South America from the Amazon to the province of Chiquitos. Might not a region be some day discovered in which ligneous fungi, _Cenomyce rangiferina_, or mosses, form high trees? _Neckera dendroïdes_, a German species of moss, is in fact arborescent, and the sight of a wood of lofty mosses could hardly afford greater astonishment to its discoverers than that experienced by Europeans at the aspect of arborescent grasses (bamboos) and the tree-ferns of the tropics, which are often equal in height to our lindens and alders. The maximum size and degree of development attainable by organic forms of any genus, whether of animals or plants, are determined by laws with which we are still unacquainted. In each of the great divisions of the animal kingdom, as insects, reptiles, crustacea, birds, fishes, or mammalia, the dimensions of the body oscillate between certain extreme limits. But these limits, based on the observations hitherto contributed to science, may be enlarged by new discoveries of species with which we are at present unacquainted.