28 BULLETIN UNITED STATES GEOLOGICAL SURVEY. [Yol.YI. 



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

 to Dakota on the east to the Sierra ISTevada and Cascade Mountains on 

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

 Tiew, except in the case 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 continuation, below the wooded 

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

 So we do not reckon Finns monopliylla,, nor Chilopsis saligna^ nor Leuco- 

 crmum, and the like, as common to the Great Basin and the Pacific 

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

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

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

 liana, nor Balea alopecuroides, nor Gollinsia parvijlora, and hardly Bubus 

 Nutkanus as constituents of the Atlantic United States flora. Such 

 limitations heighten the contrast between the compared floras, but 

 render the comparison more manageable and efl'ective, 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- 

 lected, 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. 



Ranunculace^. — Are represented on the Atlantic side by eighteen 

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

 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) verticillaris. All the genera of the Eocky Mountain 

 flora (if we except Crossosoma) are amphigsean.* Of such genera, Pcconia 

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

 Atlantic flora. The peculiar genera are Trautvetteria, Atlantic and 

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

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

 Pasonia, in two species, one which belongs to the Ariz.ouian district. 

 The species of DelpMnium increase from the Atlantic westward, and are 

 remarkably prominent in California. 



Magnoliace^. — Of three genera and eleven species in the Atlantic 

 flora ; are wholly absent from the westward floras. 



Anonace^. — Have a peculiar genus (the so-called Papaw) in the 

 Atlantic flora, but nothing to the west of it. 



* This is the most couvenient designation of the genera indigenous to Europe and 

 Northern Asia as well as to America. 



