16 UNITED STATES AND MEXICAN BOUNDARY. 
habitable condition of different sections of the country, will be dwelt on by others, or may be 
left to inference from what has been already noted. 
BOTANICAL FEATURES. 
The general botanical features of the region under examination next claim our attention, 
and in elucidating them, we shall be guided by the great natural divisions of country already 
indicated, as these furnish us plain lines of demarcation for separate botanical districts. Thus, 
` there is a group of plants growing in the immediate vicinity of the sea, and which characterize 
“the Littoral Region; above these, and confined more or less closely to the base of the mountains, 
is found another group indicating the Supra-Littoral Region; next to this, in the ascending 
order, is what may be termed the Lower Mountain Region, with a still different vegetation; and 
lastly, the Proper Mountain Region, producing plants peculiar to elevated localities. 
LITTORAL PLANTS. 
Among the exclusively littoral plants, some are common to the seacoast of nearly all 
countries; and these, such as the common Salicornia, are found here, and it is our intention to 
notice only those which are peculiar to this particular coast. We mention, first of all, two 
species of Abronia, (A. arenaria and A. umbellata,) which spread their trailing branches over 
the sand dunes which edge the sea-shore, and with their abundant foliage and beautiful 
umbelled flowers, give relief to the barren features of the landscape. 
Growing with the Abronias a species of ice-plant (Mesembryanthemum) is frequently found. 
This has spreading succulent stems and triangular leaves. Its showy, though evanescent, pink 
flowers appear only in bright sun-light, and are succeeded by an edible, juicy fruit. In the 
same region, though less closely confined to the sea-beach, is another species of this genus, 
probably identical with the well known M. crystallinum. Неге it is an annual, attaining its full 
size in the month of June, when it may be seen in large patches several rods in extent, pre- 
senting a thick bed of showy flowers. The leaves and stems are beset with shining glandular 
little warts, which contain a strongly saline fluid. The flowers, which are ephemeral and very 
abundant, appear in regular succession from June to August. After the flowering period the 
plant withers and dries up, leaving a thick mat of seed vessels, which remain closed until the 
commencement of the rainy season ; the hygrometric tissue of the capsule then expands, under 
the influence of moisture, and the enclosed seeds escape and commence germinating. The dry 
remains of the plant are frequently burned for the sake of the ashes, which, being strongly 
alkaline, are used in making soap. Both the species here mentioned are so characteristic of the 
` ` places they occupy that they would seem to be indigenous, but it is generally thought by 
fe botanists that they are introduced. 
| Among other plants characteristic of this region are GZnothera viridescens, (Hook.,) F'ranseria 
bipinnatifida, and a species of Statice, which grows near the head of San Diego bay, and seems 
hardly distinct from 5. Limonium. 
The common Salicornia here acquires a shrubby growth, and is frequently entwined with a 
species of Dodder, and accompanying it is found a new species of Batis, to which Dr. Torrey 
has given the name of B. Californica. Frankenia grandifolia grows here abundantly, associated 
with Layia carnosa, Aromia tenuifolia, and Tuckermannia. Among the shrubs peculiar to this 
