American Journey of Discovery by way of the Missouri to the Pacific, is a remark of great practical and philosophical importance, if it be well founded.
"Mr. Dunbar, (he says,) observes, that the change of colour in the leaves of vegetables, which is probably occasioned by the oxygen of the atmosphere acting on the vegetable matter, deprived of the protecting power of vital principle, may serve as an excellent guide to the naturalist who directs his attention to the discovery of new objects for the use of the dyer. For he has always remarked, that the leaves of those trees whose bark or wood is known to produce a dye, are changed in autumn to the same colour which is extracted in the dyer's vat from the woods; more especially by the use of mordants, as allum, &c. which yields oxygen: thus the foliage of the hickory and oak, which produces the quercitron bark, is changed before its fall into a beautiful
