In 1851 Dr. Weddell undertook a second voyage to South America, and in 1852 he entered the Bolivian chinchona region of Tipuani by way of Sorata. In descending the eastern slopes of the Andes he describes the vegetation as taking new forms at every mile of the descent. The undergrowth was formed of _Melastomaceæ_ with violet-coloured flowers (_Chætogastra_), myrtles, _Gaultherias_, and _Andromedas_; lower down there were many superb species of _Thibaudias_; and, where the great forests succeed to the smaller growth of the more elevated region, the predominant trees were _Escallonias_, arborescent _Eupatorias_, _Bocconias_, and a fruit-bearing _Papilionacea_ with a scarlet corolla. He encountered the first forest chinchona-trees at an elevation of 7138 feet, being the _C. ovata var. α vulgaris_. Descending still, he came to paccay-trees (_Mimosa Inga_) in flower, and met with the first plant of the shrubby variety of _C. Calisaya_, on an open grassy ridge or _pajonal_, at an elevation of 4800 feet. Dr. Weddell descended the river Tipuani to Guanay, a mission of Lecos Indians, and ascended the Coroico in a canoe made of the wood of a species of _Bombax_. The forests bordering on the river Coroico abounded in many species of palms, chiefly _Maximilianas_ and _Iriarteas_, the latter a singular kind with a trunk supported on long aërial roots. There were also many trees of _C. micrantha_ on the banks of the Coroico, a species of chinchona, the peculiarity of which is its fondness for the bottoms of valleys and banks of rivers, while most of the others prefer elevated ridges or slopes of the mountains. With it were growing trees of the beautiful _Cascarilla magnifolia_, an allied genus with deliciously fragrant flowers.