THE TRUCKEE AND HUMBOLDT VALLEYS. 29 
tion or by streams descending from the mountains, and usu- 
ally dry in the summer months. 
A desert section proper and one more particularly per- 
taining to the alkaline flats and vicinity of saline springs. 
Lastly, the flora of the mountains is naturally divided into 
two distinct fields, according as the plants grow in the caüons 
in the vieinity of water, or flourish ou the higher and more 
exposed regions where in the summer months little or no 
moisture is obtained, unless from an accidental shower, or by 
direct condensation from the atmosphere. Of course these 
divisions are more or less arbitrary and shade the one into 
the other. Following the above order we observe that on 
the, Truckee there are a few plants immediately bordering 
the river and small streams which have apparently been 
drifted from above with soil and debris swept off by floods. 
The original habitat of some of these plants, I presume to be 
the neighborhood of Lake Tahoe, although no definite data 
can be given in support of such an opinion without an 
examination of the flora near the source of the stream. 
Still, certain plants which I always found on sandy shoals 
and islands in the Truckee, ànd nowhere else, lead me to 
this conclusion. Seeds, too, have undoubtedly been trans- 
ferred from place to place through the same medium ; but 
whether; with the exceptions just mentioned, the prevalent 
plants have advanced from the east or the west, I am not 
prepared to say. It would require for the study more time 
and larger experience than it was my lot to bestow upon it. 
The species of plants found along the Truckee at one camp 
differed but slightly from those discovered at another, pre- 
serving a close resemblance to each other as far as Wads- 
worth, the limit of my investigations. It would be tedious and 
uninteresting to read a list of the plants found in this region, 
a more correct account of which will, I hope, soon be given 
to the publie by one more competent to treat of them, and 
I shall therefore only mention such as are conspicuous to 
the traveller as he passes by, or such as have a positive or 
