384 BOTANICAL GAZETTE [JUNE 
large portion of Montana, western Dakota, eastern Wyoming 
and Colorado and western Nebraska, to a transition-region, con- 
necting the prairies proper with the elevated plains of the Great 
Basin country. The eastern foothills of New Mexico are 
included by him in the steppe and desert region of Arizona. 
Topographically and phytogeographically, the foothills along 
the eastern border of the Rocky mountains are an intrinsic 
portion of the great plains, and, as such, are to be included in 
the prairie province. On the south, while extending the domain 
of the prairies to the Gulf of Mexico, Drude distinguishes the 
prairies beyond the Canadian river as southern prairies. It is 
doubtful whether he would have us consider this a region; at 
any rate he does not expressly term it such, as is the case with 
the Saskatchewan prairies. However, a glance at the flora of 
the geographical extremes of the prairie province will demon- 
strate that neither the northern nor the southern prairies are 
regionally distinct from the central mass, but that they merely 
manifest such “shading-out’”’ as is always present toward the 
confines of large vegetation-regions. 
Turf-builders are the most important vegetation-form for the 
characterization of the prairies, and in determining the floral 
contrast between regions, and the degree of such contrast, they 
are first to be considered. Of the thirty-three species of grasses 
which comprise the facies and the principal species of the prairie 
province formations, the prairies of Nebraska, Kansas, and the 
Dakotas possess the entire number; those of Saskatchewan, 
Manitoba, etc., possess thirty species; and those of the Red 
river country, twenty-nine species. From this it is seen cus the 
fundament of the floral covering of the prairie province 1s essen- 
tially homogeneous from the northern extreme to the southern 
extreme. Of the thirty-six species which constitute the ee 
tional facies of the prairies, the central prairies (central eed 
purely geographical sense) possess the full number ; the southern 
prairies thirty-one species; and the northern thirty-two it 
Of one hundred and forty species most important with respee 
to frequence, abundance, or characteristic, eighty-three .. 
