52 BULLETIN UNITED STATES GEOLOGICAL SURVEY. [FoZ.vi, 



Eocky Mountain region, yet of few genera; and are remarkably devel- 

 oped and diversified in the Pacific flora, which has thirty-three genera^, 

 several of them peculiar. Only eleven of the forty iS'orth American, 

 genera are European, but several of those otherwise peculiar are shared! 

 with Eastern Asia, especially the MelantMece. The characteristic feat- 

 ures of the Liliaceous vegetation of the two western floras are given by 

 the endemic genera, Brodicea and relatives, Leucocrinum, Chlorogalum^ 

 Galochortus, &c., by Yucca, which is also Atlantic, and bj' the great 

 development of the genus Allium, exceeded only in i!:^"orthern Asia. 



JuNCACE^. — Are numerous and well distributed over the continent^ 

 but require no special remark. 



PoNTEDERiACEiE. — Tropical aquatics, except the three genera of ther 

 Atlantic flora, one of which [Scliollera) reappears in its single species 

 on the Pacific coast. 



CoMMELYNACE^. — Also mainly tropical; are represented by two 

 genera aud several species in the Atlantic flora ; one or two of these 

 barely reach the Rocky Mountains southward ; all are absent from the 

 Pacific flora. 



XYRiDACE^iE. — Mayaca, a South American aquatic, and sixteen spe- 

 cies of Xi/ris are characteristic of the Atlantic flora; are wanting to the 

 others. 



Eriocaulone^. — Chiefly Atlantic South American; are of three- 

 genera and several species in the Atlantic flora, but none at all western. 

 The remarkable thing is that the most northern EHocaulon has effected 

 a lodgment on the coast of the British Islands. 



Oyperace^. — The number of species and genera in the Atlantic 

 flora is nearly double that of the Pacific, and the Rocky Mountain flora 

 has few. 



GrRAMiNB^, whlch would be well worth a particular analysis, are more 

 equally divided, atleasi as to genera. Of these the western floras have 

 many, chiefly of Texano-Arizonian and Mexican types, which are un- 

 known at the east. The Atlantic flora possesses a few peculiar genera,. 

 Zizania, Bracliyelytrum, Monanthochloa, Hydrocliloa, Ctenium, OrysopsiSy. 

 Graphephorum, Diarrliena (reproduced in Japan*?), Gymnostichum, Trip- 

 sacum. 



It is hardly worth while to extend this survey into the Cryi:)togamiay 

 even to the Ferns. 



The subjoined tabular view of the Phsenogamous orders presents ta 

 the eye some of the facts which the preceding pages have brought out 

 as regards respectively their presence or absence or their relative im- 

 portance in the three floras which we have been comparing. The name in 

 full capitals indicates that the order or group has its headquarters in the 

 flora of that column. Small capitals indicate a full or a notable repre- 

 sentation, at least comparatively. The name in ordinary Roman letters 

 indicates a more or less considerable representation ; in italic type, a 

 less or scanty representation ; the initial with a dash (as N in the 



