96 THE SALTON SEA. 



in fact, blind springs, and perhaps a little water may at times appear on the surface. The 

 center is mostly occupied by Typlia, with a considerable admixture of Pluchea camphoraia. 

 In this, and surrounding it, is an open thicket of slender black willows and delta cotton- 

 woods, with more or less Baccharis glutinosus. Usually there is an outer margin of Dis- 

 tichlis sod. It will be seen at once that this is a society very like that previously described 

 as growing about springs, and it might with some propriety be included with them. It is 

 differentiated, however, by the predominance of the mesophytic trees. 



SAUCETA OF IMPERIAL VALLEY. 



It has been already mentioned that the flora of the river bottoms of Imperial Valley 

 is, in part, mesophytic. This consists of small clumps of delta cottonwood, but more 

 especially of thickets of Salix. In places the same willow also appears densely bordering 

 the banks of irrigation canals. 



XEROPHYTIC FORMATION. 



It is not altogether easy to draw the line between the halophytic associations of alka- 

 line soils and the distinctly xerophytic associations, for the latter often include such typical 

 halophytes as Suceda and Spirostachys. But these are here very subordinate members in 

 the associations, most of whose characteristic plants never enter into the composition 

 of true halophytic societies. 



The xerophytic formation occupies an area exceeding the combined areas of all the 

 others, comprising, indeed, the greater part of the whole Sink. It can be divided into 

 certain a.ssociations which, while including in their composition some plants common to 

 all, yet are in other ways sufficiently differentiated. 



SOME GENERAL CHARACTERISTICS OF THE XEROPHYTIC FORMATION. 



The most marked general characteristic of the flora of southern California is the 

 prevalence of shrubs and suffrutescent plants. These are less accompanied by other 

 forms of vegetation in direct proportion to the aridity of the environment. In the Salton 

 Sink the climax is reached. The species of shrubs are few, but they constitute the greater 

 part of the whole plant population, plants of other forms being but an insignificant part 

 of the whole. 



Individual shrubs are separated by intervals often great and almost wholly bare. 

 They are dwarfed by lack of moisture; as there is no competition for sunlight, but rather 

 a need of protection from excessive insolation, they are low, compact, and more or less 

 rounded in outline, this being the shape best adapted to shelter them from the light and 

 the heat of the sun's rays, and from the evaporating effect of the strong, dry winds. This 

 is well exemplified by Larrea, which in some other parts of the desert, where the condi- 

 tions favor a social growth, attains a height of 6 feet and has a loose and open form; while 

 in the Sink it seldom exceeds 2 feet in height and is almost as compact as the garden box. 



A noticeable feature of the xerophytic vegetation of the Sink is the absence of certain 

 types of plants and certain modifications of others usually present in similar environments 

 and recognized as characteristic of arid regions. Thus, in the mountains about the 

 Sink, and almost to its very margin, in the San Gorgonio Pass down to as low as 400 feet 

 altitude, and on the summit of the broad open plain which divides it from the slope towards 

 the Colorado River, the Cactacese surround the Sink on every side, but do not enter it.' 

 So closely do certain opuntias approach the margin of the Sink, along the flanks of the 

 Chuckawalla Mountains, that there seem to be no differences of temperatiu-e, aridity, or soil 



• Near Figtree John Spring a single specimen of Echinocactus cylindracevs was seen in a wash, down which it 

 had evidently been carried from the neighboring mountains, where the species is frequent, and a solitary cylindraceoua 

 opuntia was seen near Mecca under similar conditions; but neither can be considered members of the true flora of 

 the Sink. 



