44 BULLETIN UNITED STATES GEOLOGICAL SURVEY. [Yol.Vl. 



m here restricted to the Atlantic flora. This divides (irhemhim with East- 

 ern Asia. Spigelia and Polypremum with tropical America, Mitreola with 

 both. 



GENTIANACEJB. — The Gentians, generally most numerous in mount- 

 ain districts, preponderate in our western floras; yet the Atlantic States 

 do not lack species. The amphiga-an genus Eri/threa is finely repre- 

 sented in the Pacific flora and in the Texano- Arizonian region, sparingly 

 in the Rocky Mountain region, while in the Atlantic States there is 

 probably no indigenous species north and east of Arkansas. Microrala 

 has probably reached California from South America. Mcnyanthcx tri- 

 foliata is all around the northern part of the temperate zone. 3/. crista- 

 gaUi is one of the few plants which the Pacific flora shares with that of 

 Japan. The two species of Limnanthemum are strictly Atlantic, and are 

 connected with tropical species of the eastern side of the continent. 

 ffalenia is at the same time a high-northern and an Andean genus. 

 Swertia is absent from the Atlantic side of the continent. As to the 

 peculiarly American genera, the finest is Frasera, with one Atlantic spe- 

 cies, and a few others both of the Rocky Mountains and of the Pacific 

 side of the continent. Eustoma reaches from the Texano- Arizonian 

 region just within our border over to the eastern border of the plains. 

 Sabbatia, of thirteen species, Bart&R&a, and Obolaria are wholly peculiar 

 to the Atlantic flora. 



POLEMONIACEJE. — Although not wholly absent from Europe and 

 Northern Asia, compose a truly characteristic American order, and, al- 

 though half the genera are Mexican and South American, at least niue- 

 tenths of the species must belong to the United States. Of these, an 

 equally large proportion adorn the western regions, whether the mount- 

 ains, the valleys, or the plains, under the various forms of Oilia, Col- 

 Jo 1/1 in. and Phlox. Yet, to the Atlantic States belong the herbaceous 

 perennial species of the latter genus, which have longest been known to 

 botanists. 



1 1 \ dropiiyllacI'L-'e. — This is more strictly an American, and even 

 more predominantly a Western North American, order than the pre- 

 ceding. A very Large pari of our species and forms inhabit the Rocky 

 Mountain region, chiefly its plains and valleys, and fewest the At- 

 lantic region. No genus is restricted to the latter, though into it only 

 extends the southern Hydrolea; into the lower parts of the intermediate 

 regions extends the mainly Texano-Mexican genus Wama ; to it belongs 

 Ciniinitlnis, Tricardia, and essentially Lemmonia : to it and to the Pacific 

 flora belong Emmenanthe, H&perochiron, Eriodictyon; to the Pacific- 

 Mora alone belong Draperia and Romanzoffia. 



Boeragen \( "i:.i-:. — This is a larger order, and is found all over the 

 world. The tribes or suborders other than the Borragea hardly come 



at all within our limits, excepting two or three species of l/cliofropium, 



on.- of which is very characteristic of the plains east of the Kocky Mount- 

 ains (viz, //. convolvula€eum ) the Euploca of Nuttall, and it has also 



