The Cactus melo cactus is often 10 to 12 inches in diameter, and has usually 14 ribs. The natural group of Cactaceæ, the whole family of Nopaleæ of Jussieu, belong exclusively to the New Continent. The cactuses assume a great variety of shapes: ribbed and melon-like (Melo cacti); articulated or jointed (Opuntiæ); forming upright columns or pillars (Cerei); serpentine and creeping (Rhipsalides); or provided with leaves (Pereskiæ). Many extend high up the sides of the mountains. Near the foot of the Chimborazo, in the elevated sandy plain around Riobamba, I have found a new kind of Pitahaya, the Cactus sepium, even at a height of 10,000 (10,660 Eng.) feet. (Humboldt, Bonpland, and Kunth, Synopsis Plantarum æquinoct. Orbis novi, T. iii. p. 370). [38] p. 19.--“_The scene in the Steppe is suddenly changed._” I have endeavoured to depict the coming in of the rainy season, and the signs by which it is announced. The usual deep dark azure of the sky in the tropics arises from the more complete solution of the vapour contained in the atmosphere. The cyanometer indicates a paler blue as soon as the vapours begin to be precipitated. The dark spot or patch in the constellation of the Southern Cross gradually becomes indistinct as the transparency of the atmosphere diminishes, and this alteration announces the near approach of rain. The brightness of the Magellanic clouds, (Nubecula major and minor), gradually vanishes in a similar manner. The fixed stars, which before shone like planets with a steady, tranquil, and not trembling light, now scintillate even in the zenith, where the vapours are least. (See Arago, in my Relation hist. T. i. p. 623). All these appearances are the results of the increased quantity of vapour diffused in the atmosphere. [39] p. 20.--“_Awakened from a torpid state by the first fall of rain._” Extreme dryness produces in plants and animals the same phenomena as does the withdrawal of the stimulus of heat. Many tropical trees and plants shed their leaves during the dry season. The crocodiles and other amphibious animals hide themselves in the mud, where they lie apparently dead, like animals in a state of hybernation or plunged into winter sleep by cold. (See my Relation historique, T. ii. pp. 192 and 626.) [40] p. 20.--“_The aspect of a vast inland sea._” Nowhere are these inundations more extensive than in the network of rivers formed by the Apure, the Arachuna, Pajara, Arauca, and Cabuliare. Large vessels sail across the country over the Steppe for 40 or 50 miles. [41] p. 21.--“_To the mountain plateau of Antisana._” The great mountain plain or plateau surrounding the volcano of Antisana is 2107 toises (13473 English feet), above the level of the sea. The atmospheric pressure at this elevation is so small that the wild cattle, when hunted with dogs, bleed from the nose and mouth. [42] p. 22.--“_Bera and Rastro._”