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HE session being now happily inaugurated, your presiding officer of the last year has only one duty to perform before he surrenders the chair to his successors. If allowed to borrow a simile from the language of my own profession, I might liken the President of this Association to a biennial plant. He flourishes for the year in which he comes into existence, and performs his appropriate functions as presiding officer. When the second year comes round he is expected to blossom out in an address and disappear. Each president, as he retires, is naturally expected to contribute something from his own investigations, or his own line of study; usually to discuss some particular scientific topic. Now, although I have cultivated the field of North American botany with some assiduity for more than fifty years, have reviewed our vegetable hosts, and assigned to no small number of them their name and their place in the ranks, yet, so far as our own wide country is concerned, I have been, to a great extent, a close botanist. Until this summer I had not seen the Mississippi, nor set foot upon a prairie. To gratify a natural interest, and to gain some title for addressing a body of practical explorers, I have made a pilgrimage across the continent; I have sought and viewed in their native haunts many a plant and flower which, for me, had long bloomed unseen, or only in the Hortus siccus. I have been able to see for myself what species and what form constitute the main features of the vegetation of each successive region, and record—as the vegetation unerringly does—the permanent characteristics of its climate. Passing on from the eastern district, marked by its equally-distributed rainfall, and therefore naturally forest-clad, I have seen the trees diminish in numbers, give place to wide prairies, restrict their growth to the borders of streams, and then disappear from the boundless drier plains; have seen grassy plains change into brown and sere desert—desert in the common sense, but hardly anywhere botanically so—have seen a fair growth of coniferous trees adorning the more favored slopes of a mountain-range, high enough to compel summer showers; have traversed that broad and bare elevated region shut off on both sides by high mountains from the moisture supplied by either ocean, and longitudinally intersected by sierras which seemingly remain as naked as they were born; and have reached at length the westward slopes of the high mountain-barrier, which, refreshed by the Pacific, bear the noble forests of the Sierra Nevada and the Coast Range, and among