xxiv 
BOTANY. 
embraced within the limits of the survey, and for securing a somewhat com- 
plete collection of the plants pecuHar to the different sections as well as 
seasons. 
As the area of the territory explored is occupied in nearly equal pro- 
portions by the mountain ranges and intervening valleys, so we find the vege- 
tation divided into two corresponding well-marked sections, which it will be 
best to consider separately. In order also to arrive at the Basin flora proper 
it will be necessary to distinguish those species which are peculiar to the 
extreme eastern and western bounding walls of the Basin, to the Washoe 
Mountains in Western Nevada as belonging rather to the flora of the Sierras 
and California, and to the Wahsatch and Uintas upon the east as a part of 
the somewhat distinct Rocky Mountain flora. Omitting, moreover, those 
plants which have as yet been found only in the southern portions of Nevada 
and Utah and which belong chiefly to the more desert region of Arizona 
and Southern California, the remaining species of the Catalogue may be con- 
sidered as giving a fair though by no means complete representation of the 
flora of this section of the Great Basin. 
No portion of this whole district, however desert in repute and in 
fact, is destitute of some amount of vegetation even in the driest seasons, ex- 
cepting only the alkali flats, which are usually of quite limited extent. Even 
these have frequently a scattered growth of Sarcohatus or Halostachys sur- 
mounting isolated hillocks of drifted sand, compacted by their roots and 
buried branches. This vegetation covering alike the valley plains, the graded 
incline of the mesas, the rounded foothills and the mountain slopes, possesses 
a monotonous sameness of aspect and is characterized mainly by the absence 
of trees, by the want of a grassy greensward, the wide distribution of a few 
low shrubs or half-shrubby plants to the apparent exclusion of nearly all other 
growth, and by the universally prevalent gray or dull olive color of the 
herbage. 
To the absence of trees there seems to be but a single exception, in the 
valley of the Truckee, where Populus monilifera and trichocarpa grow in con- 
sideral)le numbers in the liver bottom. Upon the Humboldt and Carson 
Rivers they are rarely found, and in the higher eastern valleys the willow- 
leaved P. halsamifera of the mountains scarcely ever follows the streams be- 
yond the limit of the foothills. So as respects the second of the charac- 
teristics mentioned, the turfing /*buflalo" or grama" grasses, which make 
