724 THE POPULAR SCIENCE MONTHLY. 



ON THE DERIVATION OF AMERICAN PLANTS. 



Bt Pkof. ASA GEAY.i 



THE 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 ajrpropriate 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 par- 

 ticular 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 bot- 

 anist. 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 num- 

 bers, 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 trav- 

 ersed that broad and bare elevated region shut off on both sides by 

 high mountains from the moisture supplied by either ocean, and longi- 

 tudinally 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 



1 Retiring Address of Prof. Gray before the American Association for the Advance- 

 ment of Science, upon resigning the presidency, at the late meeting in Dubuque, Iowa, 

 August 21, 1872. 



