But if the characteristic aspect of different portions of the earth’s surface depends conjointly on all external phenomena,--if the contours of the mountains, the physiognomy of plants and animals, the azure of the sky, the form of the clouds, and the transparency of the atmosphere, all combine in forming that general impression which is the result of the whole, yet it cannot be denied that the vegetable covering with which the whole earth is adorned is the principal element in the impression. Animal forms are deficient in mass, and the individual power of motion which animals possess, as well as often the smallness of their size, withdraw them from our sight. The vegetable forms, on the contrary, produce a greater effect by their magnitude and by their constant presence. The age of trees is marked by their size, and the union of age with the manifestation of constantly renewed vigour is a charm peculiar to the vegetable kingdom. The gigantic Dragon-tree of Orotava,[12] (as sacred in the eyes of the inhabitants of the Canaries as the olive-tree in the Citadel of Athens, or the Elm of Ephesus), the diameter of which I found, when I visited those Islands, to be more than 16 feet, had the same colossal size, when the French adventurers, the Béthencourts, conquered these gardens of the Hesperides in the beginning of the fifteenth century; yet it still flourishes, as if in perpetual youth, bearing flowers and fruit. A tropical forest of Hymenæas and Cæsalpinieæ may perhaps present to us a monument of more than a thousand years’ standing.