PLANT ECOLOGY AND FLORISTICS OF SALTON SINK. 95 



the wind. These increase in size with the distance from the shore line. It is a condition 

 which soon proves fatal to Sesuvium, so that the outer and drier soil is left to the more 

 resistant Spirostachys. Among these drier mounds Astragalus limatus grows in consider- 

 able abundance, and a little Oligomeris glaucescens appears as an interval plant. 



HALOPHYTIC ASSOCIATIONS OF THE RIVER BOTTOMS. 



When the interval between the bluff banks of the rivers is sufficiently wide, it is occu- 

 pied by low bottoms, little above the water-level of the channel which winds through 

 them, the whole wet or damp in proportion to the distance from the stream. The paludose 

 associations which occupy the immediate margins of the streams have already been de- 

 scribed. The remaining vegetation consists of halophytic and mesophytic plants, fairly 

 well segregated in small societies in the wider bottoms, but much confused in the narrower 

 ones. The mesophytic element, consisting of willows and cottonwoods, will be considered 

 later. The halophytic societies occupy open intervals which are probably due to soil 

 conditions. Sida hederacea holds possession of some of these. The individuals are small, 

 the declined stems seldom over 6 inches long, and usually the individuals are separated 

 by an inch or two of bare soil. Lippia nodiflora covers small tracts, but covers them 

 compactly, since the stems root at the nodes and continually spread. Alriplex fasciculata, 

 an herbaceous species with prostrate stems, a foot or less in length, is a component of these 

 associations. Other less prominent members are Dicorca canescens, a bushy annual, 

 Sesuvium, and all the chenopods of the Indio-Mecca flats. 



SESUV1UM-PHRAGM1TES ASSOCIATION OF SALT SLOUGH. 



The so-called Salt Slough is a dry wash, heading in the playa below Dos Palmas and 

 reaching Salton Sea near the Salton railway station, a mere section house. It is at this 

 point quite deep, with bluff banks of clay, and at the present stage of the sea it forms an 

 inlet of it. From one of the banks a seepage of salty water serves to moisten a strip along 

 its base, so that there is a narrow, more or less muddy bottom, to the maintenance of which 

 the water of the inlet doubtless contributes. 



The vegetation is disposed in the following manner : The wettest part of the seepage 

 soil, close to the bluff, is occupied by Scirpus paludosus, but this does not enter the water 

 of the inlet, which is bordered by a shore entirely bare, a feature doubtless due to the rapid 

 recession of the water. The greater part of the flat is spread with broad circular mats of 

 Sesuvium, some of them as much as 6 feet in diameter; with this grows Heliotropium 

 curassavicum, a semi-succulent herb. This, in turn, is bordered by a fringe of Phragynites 

 communis, which throws out an abundance of stout stolons, 6 or 8 feet long, wandering 

 over the surface of the sand without taking root. 



MESOPHYTIC FORMATION. 



As will be readily inferred from the climatic conditions, mesophytes are but poorly 

 represented in the flora of the Sink. Even those plants which must be included in this 

 class possess certain xerophytic characteristics. The leaves of the delta Cottonwood are 

 but half the size of those of the Cottonwood of cismontane California. The leaves of the 

 willows are very narrow and have a circularized epidermis. Baccharis glutinosus, also a 

 narrow-leaved species, has the surface of its leaves protected by the varnish which sug- 

 gested its specific name. Yet these few are all the plants which, by any construing of the 

 term, can be reckoned as mesophytes. 



MESOPHYTIC ISLETS IN THE MECCA FLATS. 



In the lower end of the Indio-Mecca flats, and mostly in the parts occupied by Atriplex 

 lentiformis, there occur small tracts of mire, covered with a surface layer of firmer soil, 

 which yields under the foot, and through which animals are likely to break. They are, 



