336 Vegetation in Nevada and Arizona. [June, 
on the methods used for making histological and embryological 
preparations. The account here given applies, of course, to the 
best laboratories, but they do not all offer the same great ad- 
vantages. : 
—— ee 
THE DISTRIBUTION OF VEGETATION IN PORTIONS OF 
NEVADA AND ARIZONA. 
- BY W. J. HOFFMAN, M. D. 
j a flora of Nevada may be divided into four distinct classes, 
namely : — 
I. The flora of the mountains. 
II. The flora of the foot-hills. 
III. The flora of the plains. 
IV. The flora of the salt marshes. 
In the lower two thirds of Nevada and the northwestern por- 
tion of Arizona, from latitude 41° 40’ N., at Bull Run Mountain, 
southward to latitude 35° 20’ N., we have a country composed of 
a series of plains and deserts surrounded by a net-work of mount- 
ain chains. The more northern valleys are composed of tolera- 
bly good soil, but as we proceed southward they become more 
and more sandy, and contain a greater amount of saline ingre- 
dients. There is every evidence that many of these basins were 
at one time inland seas, but owing to the rapid evaporation and 
absence of aqueous precipitation, they have in the greater num- 
ber of instances become dry, leaving their solid ingredients as the 
soil of the deserts, as in Diamond Valley, Death Valley, etc., oF 
there may still remain sufficient moisture to cause salt marshes, 
as Armagosa Desert and that at Silver Peak which covers an 
area of only about eight or nine hundred square miles of mud 
and salt. A great deal of the alkalinity of some regions is de- 
rived from the mountains. During the disintegration of feld- 
spathic rocks, the soluble salts are slowly carried down to add to 
the sterility of the valleys. Rain seldom falls on the plains, but 
the more prominent peaks are subject to showers nearly every 
afternoon. Peaks whose altitude exceeds that of the timber-line 
are most frequently visited. The causes are, the air om 
heated on the deserts (as in Death Valley we recorded 120° in 
the shade at from two to half past three o’clock) rises towards 
the cooler summits'‘of the mountains, when condensation of vapor 
terminates in precipitation, the heavy clouds charged with elec- 
tricity hanging over the mountains for an hour or two, usually 
