No.l.] GRAY AND HOOKER ON THE ROCKY MOUNTAIN FLORA. 55 



The groups in this tabulation, it will be observed, have not all the 

 rank of orders. Such as they ar^, the— 



Atlantic flora has 156 



Eocky Mountain flora (in most extensive sense) 112 



Pacific flora 127 



But of the groups very slightly represented there is only one in the 

 first, while there are twenty-four in the Eocky Mountain flora and fifteen 

 in the Pacific. If these be omitted the greater diversification of the At- 

 lantic flora will be the more apparent — 



Atlantic orders or groups 155 



Eocky Mountain 88 



Pacific 112 



As to the numerical extent, respectively, of these three great divisions 

 of the United States flora, exactness would be attainable only through 

 much labor ; and an approximation is nearly as valuable as would be a 

 close count from present and still changing data. Mann's Catalogue of 

 the Phienogamous Plants of the United States east of the Mississippi, 

 may be taken for the Atlantic flora, excluding for our purpose the intro- 

 duced species and those of the Florida peninsula. The official Botany 

 of California, mainly by S. Watson, now just completed, includes or men- 

 tions the greater part of the Pacific species and genera, but includes 

 many which, though indigenous to that State or near its borders, really 

 pertain only to the flora of the interior basin. Mr. Watson's careful 

 elaboration of the botany of this basin and its borders, presented in his 

 volume (V.) of Clarence King's Explorations and Surveys on tlie For- 

 tieth Parallel, sums up and analyzes the vegetation of this district; but 



