94 THE SALTON SEA. 



as dominants they are able to hold possession only of soils too alkaline to permit the growth 

 of the latter. In tracts so heavily charged as to inhibit all the other chenopods of the 

 flats, Spirostachys holds undisputed possession. Here it forms a low, sparse growth, the 

 individuals separated one from the other by intervals of bare, alkaline-incrusted soil. 

 The stress of the conditions is indicated by the dwarfing of the plants, hardly a foot high, 

 and by the yellowish color of the foliage, in striking contrast to the dark green of the vigor- 

 ous bushes two or three times their size which flourish under more favorable conditions. 



Forms of Isocoma veneta var. acradenia, a many-flowered composite, appear as subordi- 

 nate members of all of the associations which have been passed in review. Occasionally, in 

 drier and sandier spots, they form a pure growth, marked, among their somber neighbors, 

 by the bright yellow of their abundant autumnal blossoms. In a variety of unstable eco- 

 logical forms, some of which have received names as species, Isocoma veneta is the most 

 widely distributed plant of the desert. In other forms it is found in all except the moun- 

 tainous parts of southern California. Its value as a phyto-geographical index is, therefore, 

 inconsiderable. In the drier parts of these alkaline flats it attains its greatest size and its 

 most abundant inflorescence. It is here several-stemmed, and the clusters of a few heads, 

 borne on pedicles 1 or 2 inches long, are produced in large open panicles. 



In all these associations there is a singular dearth of herbaceous plants. A not infre- 

 quent Heliotropium curassavicum spreading over the ground and an occasional Conyza 

 coulteri are the only species of any importance. 



Not less than five trees grow in this formation, but a consideration of them is reserved 

 for a subsequent page. 



HALOPHYTIC ASSOCIATIONS OF IMPERIAL VALLEY. 



The southern extremity of the Sink also has its halophytic associations, whose char- 

 acter varies in accordance with the nature of the soil. The plains of compact Imperial 

 clays receive but little water from any source, and this little they absorb with difficulty 

 and lose with rapidity. The water-table is far below the limited capillary capacity of the 

 soil. In many places the percentage of alkali is considerable. The factors inimical to 

 vegetable life are at the maximum, and there are wide expanses absolutely devoid of a 

 single plant save in the infrequent furrows and channels which constitute the drainage 

 system. In these the passage of the water has somewhat leached the soil and rendered it 

 more open and retentive. Here scattered and stunted suffrutescent plants are able to 

 exist. Mainly they are Suceda, reduced to a low and compact form, with an occasional 

 equally stunted Atriplex canescens. In the minor drain furrows the plants are fewest and 

 smallest, and their number and development, never great, increases in proportion to the 

 size of the channel and the consequent greater leaching effect of the water discharged 

 through it. 



A second association, which the railway traveler may observe near Estelle, is com- 

 posed of Spirostachys, growing at intervals of 4 to 10 feet, each the center of a small mound, 

 built up, to all appearance, by wind action. The intervals are flat and perfectly free from 

 vegetation. 



Other parts of these flats are occupied by an open growth of Suceda, usually inter- 

 mixed with more or less Atriplex canescens. This soil has a less alkaline appearance and 

 probably a less alkaline content, for when reclaimed and irrigated it is considered suitable 

 for agriculture. 



SESUVIUM-SPIROSTACHYS ASSOCIATION. 



At points on the southeastern borders of Salton Sea, where the ground is moist and 

 moderately alkaline, the zone nearest the water is covered with Sesumum sessile growing 

 in large, prostrate mats, circular in shape. Behind this is a mixed zone of Sesuvium and 

 Spirostachys, both growing up through mounds which have been heaped about them by 



