The _Cactus_ form[90], on the other hand, is almost peculiar to the new continent; it is sometimes globular, sometimes articulated, sometimes rising in tall polygonal columns not unlike organ-pipes. This group forms the most striking contrast with the Lily and Banana families, and belongs to that class of plants which Bernardin de St. Pierre felicitously terms vegetable fountains of the Desert. In the parched arid plains of South America, the thirsting animals eagerly seek the _Melon-cactus_, a globular plant half-buried in the dry sand, whose succulent interior is concealed by formidable prickles. The stems of the columnar cactus attain a height of more than 30 feet; their candelabra-like ramifications, frequently covered with lichens, reminding the traveller, by some analogy in their physiognomy, of certain of the African Euphorbias. While these plants form green Oases in the barren desert, the Orchideæ[91] shed beauty over the most desolate rocky clefts, and the seared and blackened stems of those tropical trees which have been discoloured by the action of light. The _Vanilla_ form is distinguished by its light green succulent leaves, and by its variegated and singularly shaped blossoms. Some of the orchideous flowers resemble in shape winged insects, while others look like birds, attracted by the fragrance of the honey vessels. An entire life would not suffice to enable an artist, although limiting himself to the specimens afforded by one circumscribed region, to depict the splendid Orchideæ which embellish the deep alpine valleys of the Peruvian Andes. The form of the Casuarineæ[92], leafless, like almost all the species of Cactus, comprises a group of trees having branches resembling the Equisetum, and is peculiar to the islands of the Pacific and to the East Indies. Traces of this type, which is certainly more singular than beautiful, may however be found in other regions of the earth. Plumier’s _Equisetum altissimum_, Forskäl’s _Ephedra aphylla_ of North Africa, the Peruvian _Colletia_, and the Siberian _Calligonum Pallasia_, are nearly allied to the form of the Casuarinas. While the Banana form presents us with the greatest degree of expansion, the Casuarinas and the acicular-leaved[93] trees exhibit the greatest contraction of the leaf-vessels. Pines, Thujas, and Cypresses constitute a northern form but rarely met with in the tropics and in some coniferæ (_Dammara Salisburia_), the leaves are both broad and acicular. Their evergreen foliage enlivens the gloom of the dreary winter landscape, while it proclaims to the natives of the polar regions that, although snow and ice cover the surface, the inner life of plants, like the Promethean fire, is never wholly extinct on our planet.