100 BOTANICAL FEATURES OF NORTH AMERICAN DESERTS. 
HISTORICAL. 
The current conceptions of deserts are neither adequate nor correct, 
if the descriptions in the best dictionaries and cyclopedias are to be taken 
as an index. A work of wide circulation and use defines a desert as “A 
region that is wholly or approximately without vegetation. Such regions 
are rainless, usually sandy, and commonly not habitable.” Another 
characterizes a desert as ‘‘A region of considerable extent which is almost 
if not quite destitute of vegetation, and hence uninhabited, chiefly on 
account of an insufficient supply of rain; as the Desert of Sahara; the 
Great American Desert. The presence of large quantities of movable 
sand on the surface adds to the desert character of a region. The word 
is chiefly and almost exclusively used with reference to certain regions in 
Arabia and northern Africa and others lying in central Asia. The only 
region in North America to which the term is applied is the Great Ameri- 
can Desert, a tract of country south and west of the Great Salt Lake, once 
occupied by the waters of that lake when they extended over a much 
larger area than they now occupy. The name Great American Desert was 
originally given to the unexplored region lying beyond the Mississippi 
without any special designation of its limits’ (fig. 6). 
The insufficiency of the above descriptions obviously rests upon faulty 
observations and upon the failure to recognize the fact that the habit- 
ability of a region is no criterion of its arid character. The development 
of modern methods of transportation has made possible the maintenance 
of dwellings and towns with a considerable population at 1oo or even 
200 miles from the nearest supply of water. Also such facilities are not 
necessary to the sustenance of a population in deserts of the most extreme 
type as illustrated by the Sahara, which has a population of 2,500,000 
people. So far as the vegetation is concerned, the actual number of indi- 
viduals is much less than on a similar area in a moist climate; this in fact 
is one of the chief characteristics of a desert, but it would not be safe to 
estimate the total number of species much below the average number. 
Lastly, be it remembered that local topography has but little influence 
on the desert character of a region. Sandy flats, plains, valleys, and 
rocky hills reaching to such altitudes as to become mountains are included 
in some desert tracts. It follows, as a natural consequence of the sparse 
vegetation as one factor, that the surface layers of the substratum, being 
usually dry in arid regions, are readily shifted and worn by winds. 
The designation of the vast region between the Missouri River and the 
Rocky Mountains as the Great American Desert rested upon a lack of 
definite knowledge by the earlier geographers, which was shown by text- 
books as recently as 1843. Later, when the more exact results of the 
earlier explorations and surveys became known, the more important 
arid regions were fairly well delimited, and the desert areas in the Bad 
