In the morning of May 3rd I continued my attempts to cross the river, by stripping and trying the water for a ford at several points, with a long pole as a support. But the water was deep, much swollen, and very rapid; and, after having twice been as nearly as possible carried away by the fury of the stream, I was obliged unwillingly to give up the attempt for the present. I considered it prudent also to remove our encampment from the island, and to establish it on a narrow beach overshadowed by the forest, at the point where the muddy waters of the Yana-mayu unite with those of the Tambopata. These arrangements having been made, we devoted the day to an examination of the adjacent forest. The spot on which we were encamped was about 4600 feet above the sea. Our tent was pitched close to the foaming torrent, and behind rose up the tall dark forests. In front were the steep green sides of the Yana-mayu ravine, while looking down the river the view was bounded by forest-covered mountains, surmounted by the lofty peak of Corimamani. On the actual banks of the river there were trees of _C. micrantha_, with large bunches of lovely and deliciously sweet white flowers; many _carhua-carhua blancas_; and a chinchonaceous tree, which Martinez called _Huiñapu_. The _Huiñapu_ grows low down and near the banks of rivers. Its capsules are three inches long; and the veins of the leaves are a pale purple. Dr. Weddell tells me that he recollects gathering the leaves of the _Huiñapu_, and that he took it to be a variety of _Cascarilla magnifolia_. We commenced the day's work in the forest on the south-west slopes of the Yana-mayu ravine, scrambling up the steep forest-covered declivity amongst palms, tree-ferns, bamboos, and trees with buttressed trunks of stupendous size. Here too were the vast leaves of the _sayal_ palm. At a height of 400 feet above the river the _Calisaya_ region commences; while in the lower belt, from the river banks to a height of 400 feet, the most abundant chinchonaceous plant is the _Carhua-carhua grande_ (_Cascarilla Carua_, Wedd.), with very fragrant white flowers. I met with flowers and capsules together on the same tree, which is forty feet high, with a thick trunk, fine spreading branches, and masses of beautiful white flowers. I found that the _C. Calisaya_ region extended in a belt from 450 to 650 feet above the banks of the river; bamboos, large palms, _C. micranthas_, _Huiñapus_, _Lasionemas_, and the _Cascarilla carua_ being found below that line, and other species of chinchonæ and chinchonaceous plants above it. We collected twenty-five _Calisaya_-plants, two of them fine strong seedlings, and the remainder root-shoots springing up from trees which had been cut down by _cascarilleros_ in former times, but with good spreading roots of their own. The search was exceedingly hard work, scrambling through matted undergrowth, and up steep ascents, through masses of rotting vegetation.