"Jb BULLETIN UNITED STATES GEOLOGICAL SURVEY. Wol.Yi. 



the broad district between them, stretching from the plains of Arkansas 

 to Dakota oil the cast to the Sierra Nevada and Cascade Mountains on 

 the west. Then the alpine vegetation, already treated of, is left oat of 

 view, except in the ease of endemic genera or forms not belonging to 

 to the arctic-alpine flora. And it must be kept in mind that the eastern 

 slopes and outliers of the Sierra and its cont innation, below the wooded 

 portions, belong to the Great Basin or to the region reckoned with it. 

 So we do not reckon Pinua monophyUa, nor Chilopsis saligna, nor Leuco- 

 cri)ium, and the like, as common to the Great Basin and the Pacific 

 floras, bnl as pertaining to the former only; and generally we do not 

 bake account of species which merely overpass the border of the region 

 they belong to. For example, we should not reckon Anemone Nuttal- 

 liana, nor Dalea alopecuroides, nor Gollinsia parviflora, and hardly Eubus 

 Xutk«nus as constituents of the Atlantic United States flora. Such 

 limitations heighten the contrast between the compared floras, but 

 render the comparison more manageable and effective, and also, as to the 

 broad outlines, really more faithful to nature than they would be if the 

 materials were indiscriminately collected from the descriptive books and 

 every denizen of the frontiers regarded as a true citizen. 



All naturalized plants and weeds of cultivation are, of course, neg- 

 lect ed, including such as may be of American origin but which have 

 accompanied man, even the aborigines of the country, almost everywhere. 

 They belong to no particular flora, or at least are not characteristic of 

 any. 



The natural orders may be taken up seriatim. 



IvANUNCULACE^s. — Are represented on the Atlantic side by eighteen 

 genera, on the Pacific by fourteen, in the intermediate region (theEocky 

 Mountain flora in the broadest sense) by twelve. The species are in 

 nearly the same relative proportion, and a considerable number are com- 

 mon even to all three floras, the most striking case of this being that of 

 Clematis (Atragene) vertidllaris. All the genera of the Rocky Mountain 

 flora (if we except Oro8808oma) are amphigoean.* Of such genera, Pceonia 

 is peculiar to the Pacific, and Hepatioa (if ranked as a genus) only to the 

 Atlantic flora. The peculiar genera are Trautvetteria, Atlantic and 

 Pacific; Hydrastis and Xanthorrhiza, wholly Alleghanian; and Cros- 

 sosoma of California, a genus of dubious affinity, but probably nearest 

 Pceonia, in two species, one which belongs to the Arizonian district. 

 The species Of Delphinium increase from the Atlantic westward, and are 

 remarkably prominent in California. 



M A.GNOL1 \ci:.i:. — Of three genera and eleven species in the Atlantic 

 flora; are wholly absent from the westward floras. 



Axn.NAci:.];. — Have a peculiar genus (the so-called Papaw) in the 

 At hint i<- flora, but nothing to the west of it. 



• Thia i> the mod convenienl designation of the genera indigenous to Europe and 

 Northern ksia as woll as i«> America. 



