Niger flora : or an enumeration of the plants of western tropical Africa, collected by the late Dr. Theodore Vogel, botanist to the voyage of the expedition sent by Her Britannic Majesty to the river Niger in 1841 / under the command of Capt. H.D. Trotter including Spicilegia Gorgonea by P. B. Webb, and Flora Nigritiana by Dr. J. D. Hooker and George Bentham ; with a sketch of the life of Dr. Vogel ; edited by W.J. Hooker