MOVEMENTS OF VEGETATION IN THE SALTON SINK. 167 



fluctuating about a fixed level. In the Salton the water receded at such rate that during 

 the time of maximum evaporation in May or June a strip more than a yard in width would 

 be bared permanently, and seeds of all kinds in motion at that time might fall on it and 

 germinate. All other physical conditions now were minor to the fact that the soil began 

 to desiccate toward a soil-moisture content equivalent to that of the surrounding desert. 

 Occasionally small flat places or shallow depressions in the soil would be occupied by a 

 growth of Spirulina, which with the drying of the soil would, with the surface layer of the 

 soil a few millimetres in thickness, break into innumerable concave fragments, but this 

 was not followed by any definite procedure. 



The main facts of interest on the shores centered about the survival of the initial 

 sowings on the beaches, the later introductions being for the most part only of minor im- 

 portance. The chief features of the endurance of the initial forms and of the appearance of 

 additional species on the beaches after the first year may be best illustrated by a recapitu- 

 lation of the observations on the two beaches taken for the discussion of initial occupation, 

 the Imperial Junction Beach and the Travertine Terraces. 



The emersion of 1907 at Imperial Beach bore Atriplex canescens, A. fasciculata, A. 

 linearis, A. polycarpa, Amaranthis, Baccharis, Cucurbita, Distichlis, Lepidium, Leptochloa, 

 Heliotr opium, Oligomeris, Pluchea sericea, Sesuvium, Spirostachys, and Suada early in 1908. 

 Late in 1908 Amaranthus, Baccharis, Distichlis, Heliotropium, Oligomeris, Rumex, Sesuvium, 

 and Typha had disappeared. Late in 1909 Atriplex canescens, A. fasciculatus, Su(rda, 

 Pluchea sericea, Spirostachys, and Cucurbita still survived, while a secondary introduction 

 of Baccharis and of Chenopodium had taken place, both being represented by only a few 

 individuals, and these did not maintain themselves. 



Atriplex canescens, A. fasciculata, and Spirostachys had multiplied and thrived in 

 1910, while Suceda seemed to have not multiplied; Pluchea was losing a large share of its 

 individuals as a result of the desiccation. The census in 1911 was practically that of 1910 

 with the added losses of Pluchea, and no change in the balance was visible late in 1912. 

 The original sowing of this place included 17 species, 8 of which had disappeared within a 

 year; one of the remaining 8 was lost in the following year, and two of the original pioneers 

 were reintroduced only to disappear quickly. The census showed only 5 species in 1910, 

 all of which were still in evidence in 1912, but with Pluchea sericea losing ground. The 

 full return of the area to the conditions prevailing up the slope might bring in Franseria 

 or an occasional Larrea or Olneya, while the number of individuals of the other species 

 would be reduced on account of the diminished soil-moisture supply. It is to be noted 

 that the changes here are wholly and directly connected with the water supply, and that 

 the survivors are halophytes, one of which was undergoing deterioration by reason of the 

 inadequate supply. 



The original introductions on the emersions of 1907 of the Travertine Terraces com- 

 prised two species, Atriplex canescens (from seeds which had fallen down a caving bank) 

 and Phragmites (which had washed ashore as a rhizome). The cut bank may have figured 

 as a mechanical trap for grounding wind-borne seeds, or some other condition may have 

 come in, for now Atriplex polycarpa, A. canescens (re-introduced), Boideloua, Astragalus, Dis- 

 tichlis, Heliotropium, Juncus, Pluchea camphorata, Prosopis pubescens, Phragmites, Sesuvium, 

 Spirostachys, and Suceda (13 in all) were present. The place was not seen again until October 

 1910, when only Distichlis, Prosopis pubescens, Phragmites, and Astragalus remained. 



Late in 1911 Astragalus was not found, although as an annual its seeds were probably 

 present, while Pluchea sericea and Salix nigra had come in, making 5 species with another 

 probably present. Late in 1912 all of the above elements had come in except Salix and 

 Isocoma, while a single small plant of Prosopis glandulosa was recognized, which had prob- 

 ably been confused with P. pubescens, up to that time. The surface was fully occupied, 

 and of the six species present it seemed likely that Phragmites, Distichlis, and Pluchea would 



