20) ; UNITED `STATES AND MEXICAN BOUNDARY. 
tomentellus, Benth. P1. Hartweg,) a species which appears to have a wide geographical range. 
Mr. Hartweg’s specimens were collected among the mountains of the Sacramento valley, and 
we have seen others which were found by Dr. A. Randall near the head waters of the 
Gila river. 
In the more southern portions of this district, and growing very abundantly in the vicinity 
of the boundary line, we find the pretty Adenostoma sparsifolia, (Torr. in Emory’s report.) This 
grows more plentifully among the mountains than the already mentioned A. fasciculata, though 
the two agree closely in habit and are frequently found side by side. It grows in clumps, 
formed of numerous slender branches, and attains a height of four or eight feet. The upper 
part of each branch divides near the summit into a fine spray, clothed with yellowish green 
leaves, and, in the proper season, thickly set with small white flowers. The leaves and upper 
stems are covered with a glandular varnish, which exhales a pleasant aroma resembling that 
of Aspidium fragrans. 
. Other shrubs that may be noticed as characteristic of this region are the Lriodyction Califor- 
nicum and Chamæbatia foliolosa, (Benth.;) the latter recently figured by Torrey in Plantae 
Frémontianae, in the Smithsonian Contributions. The shrubbery of this district is marked 
by a very intricate mode of growth, especially that upon the Coast Range of mountains. 
Here, so densely interwoven is the close mass of stunted bushes, that it is nearly impossible to 
force one’s way either up or down the mountain sides. 
This region furnishes a large variety of herbaceous plants. The greater number of those 
which, in the accompanying list, are referred to the 55 Mountains east of San Diego,” have their 
localities in this district. Among the crevices of rocks grow several species of ferns, of the 
genera Aspidium, Gymnogramma, Cryptogramma, Adiantum, Woodwardia, &c. Mosses are 
rare, and but few lichens are observed ; among the latter are the singular Ramalina Menziesii, 
Taylor, (ZR. retiformis, Menzies,) and species of Parmelia, Roccella, and Evernia. 
THE PROPER MOUNTAIN REGION. 
The immediate summit ridge, which is elevated to a height of from 3,000 to 5,000 feet above 
the sea, bears a rather meagre fringe of pines and other trees of the same family. This im- 
parts a péculiar feature to the landscape, and recalls to mind the snows and wintry climate of 
high latitudes. Of the genus Pinus proper we find four species, some of them being dwarfed 
representatives of those forest monarchs which are so abundant and conspicuons further to the 
north. | 
In this region we encounter, though rarely, the majestic Pinus Lambertiana , With its enormous 
drooping cones. P. Sabiniana is more abundant. This species is remarkable for its singular 
fruit, each scale of which is tipped with a hard curved spine. Тһе size and shape of this fruit 
are much like that of the pine apple. 
Another species, P. deflexa, (Torr.,) has a trunk of elegant columnar form, and frequently 
attains to majestic proportions, even in these unfavorable situations. The fourth species is а 
nut-pine, and is described by Dr. Torrey in the accompanying enumeration as Pinus Llaveana. 
This species is somewhat isolated in habit, and, as far as we have ascertained, has a very 
limited range near the dividing ridge and south of the boundary line. In the character of its 
fruit and foliage this species is closely allied to Pinus monophylla, (Torr.,) though quite dis- 
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