The family of Aroideæ is there represented by the _Pothos_, whose fleshy and herbaceous stems are surmounted by leaves sometimes arrow-headed, sometimes digitate or elongated, and always divided by thick cord-like nerves. We know that the Aroideæ alone possess, in the vegetable kingdom, the property of disengaging, while flowering, a heat appreciable by the thermometer. To this family belong the _Caladiums_, a genus closely allied to the Pothos. With these lianas mingle the branching stems of the Passifloræ, or Passion-Flowers, so named because Pierre de Ceza, in his "Histoire du Pérou," asserted that he had recognized in the fantastic flowers of this genus of plants all the instruments of our Saviour's Passion--an idea which could only have been conceived by an imaginative and credulous Spaniard. Elsewhere the Bignonias open by hundreds their large and richly-coloured flowers; the Bauhinias stretch along the trees their long leafless branches, often 40 to 45 feet in length, which sometimes hang vertically from the lofty summits of the Swietenias, or Mahogany trees, and sometimes extend obliquely from one huge trunk to another, like the ropes of a ship. The Tiger-Cats, says Humboldt, display a wonderful agility in mounting or descending these graceful vegetable shrouds. Upon the umbrageous banks of the Rio Magdalena grows a creeping _Aristolochus_, whose flowers in their extraordinary development surpass those of the _Rafflesia Arnoldi_, measuring often three feet and a half in circumference. The forests of which we are now speaking also nourish numerous species of Convolvulus; I may particularize the _Convolvulus batatas_, a climbing plant, whose roots produce the feculent and saccharine tubercules known over the wide world by the name of "Patates," and frequently but erroneously confounded with that most useful vegetable, the Potato. The root of another Convolvulus, a native of Mexico, constitutes the _Jalap officinalis_, which figures in the veterinary pharmacopoeia as an important purgative.