The form of ferns, as well as that of grasses, becomes ennobled in the hotter parts of the globe. Arborescent ferns, when they reach a height of above forty feet, have something of a palm-like appearance; but their stems are less slender, shorter, and more rough and scaly than those of palms. Their foliage is more delicate, of a thinner and more transparent texture, and the minutely indented margins of the fronds are finely and sharply cut. Tree ferns belong almost entirely to the tropical zone, but in that zone they seek by preference the more tempered heat of a moderate elevation above the level of the sea, and mountains two or three thousand feet high may be regarded as their principal seat. In South America the arborescent ferns are usually associated with the tree which has conferred such benefits on mankind by its fever-healing bark. Both indicate by their presence the happy region where reigns a soft, perpetual spring. I will next name the form of Liliaceous plants (Amaryllis, Ixia, Gladiolus, Pancratium), with their flag-like leaves and superb blossoms, of which southern Africa is the principal country; also the willow form, which is indigenous in all parts of the globe, and is represented in the elevated plains of Quito (not in the shape of the leaves, but in that of the ramification), by Schinus Molle; Mytraceæ (Metrosideros, Eucalyptus, Escallonia myrtilloides); Melastomaceæ, and the laurel form. It is under the burning rays of a tropical sun that vegetation displays its most majestic forms. In the cold north the bark of trees is covered with lichens and mosses, while between the tropics the Cymbidium and fragrant vanilla enliven the trunks of the Anacardia and of the gigantic fig-trees. The fresh verdure of the Pothos leaves and of the Dracontia contrasts with the many colored flowers of the Orchideæ; Climbing Bauhinias, Passifloras, and yellow flowering Banisterias twine round the trunks of the forest trees. Delicate blossoms spring from the roots of the Theobroma, and from the thick and rough bark of the Crescentias and the Gustavia. In the midst of this profusion of flowers and fruits, and in the luxuriant intertwinings of the climbing plants, the naturalist often finds it difficult to discover to which stem the different leaves and flowers really belong. A single tree adorned with Paullinias, Bignonias, and Dendrobium forms a group of plants which, if disentangled and separated, would cover a considerable space of ground.