278 GEOGEAPHICAL DISTRIBUTION OF PLANTS. 



numerous family of plants, and are more than double the 

 Graminece. The Cruciferai come next to the Cyperacea 

 in this zone. In the polar regions beyond the continent, 

 the CrucifercB take the first place in respect of number of 

 species, then come the Graminece, which are closely fol- 

 lowed by the Saxifragece. 



The third, or prairie district, has the prevailing aspect of 

 a grassy plain, the herbage, however, having a considerable 

 intermixture of carices among the true grasses. The 

 herbage grows up rather wiry in the dry summers of that 

 region ; but, in consequence of the fires that frequently 

 spread over vast tracts, a young growth takes place, to 

 which the bison and deer resort. On the Arkansas, the 

 " buffalo or bison grass " is the Sesleria dactyloides. 

 Whether this species extends to the Saskatchewan or not, 

 I am unable to say : we certainly did not gather it there ; 

 but at the time that Mr. Drummond and I visited that 

 part of the prairie, recent fires had made flowering speci- 

 mens of grasses very rare. Of the phasnogamous prairie 

 plants actually collected, the Graminece form about the 

 eleventh, and the Cyperaceai the sixteenth. On the plains 

 the Composite are numerous and showy ; there is a con- 

 siderable variety of handsome Leguminosce, with some pretty 

 Boraginece ; and the Artemisia, owing to the quantity of 

 surface they cover, though the species are not numerous, 

 contribute greatly to the hoary aspect of the prairie vegeta- 

 tion. The Rosacea vie with the Cyperacece in number of 

 species ; but many of them are fruit-bearing shrubs, growing 

 on the banks of the rivers that serpentine among alluvial 

 points, in channels sunk deeply below the general surface 

 of the prairie. 



Between the 32nd and 33rd parallels, on the Gila and Rio 

 del Norte, west of the Rocky Mountain ridge, Colonel Emory 

 gathered many examples of Cacti, of which Dr. Engelman 



