MOVEMENTS OF VEGETATION IN THE SALTON SINK. 131 



in February 1908, included Oligomeris glaucescens, Chenopodium murale, Atriplex fasciculata, 

 A. kntiformis, Heliotropium curassavicum, and an unrecognizable species. In May the addi- 

 tional species of Baccharis glutinosa, Oenothera, Sonchus asper, Conyza coulteri, probably 

 Pluchea camphorata, and Distichlis spicata were noted. The survivors in 1912 were the 

 two species of Atriplex, Pluchea sericea (which had come in meanwhile), Distichlis, and 

 Prosopis pubescens, which had probably come up from stems or seeds left in place. 



Phragmites was the sole water-borne introduction to the Travertine Terraces of 1907, 

 seen early in 1908, and Atriplex canescens had fallen down the slope and germinated. In 

 November 1908 the population had increased to include 16 species (see page 128), but a 

 census of the area in 1910 showed but 6 species, 5 of which had maintained themselves 

 until June 1912, the soil moisture being influenced to some extent by a hemmed underflow. 

 A single innovation, Isocoma, was of recent date. 



The emersed zone of 1907 on Obsidian Island was found to bear 25 species when 

 examined in February 1908 and an additional species was added to the population at the 

 next census in November of the same year, which meanwhile had suffered a loss of 14 

 species. A year later the population of the zone had fallen to 7 species, and in October 

 1910 but 6 were present; 10 species were found here in 1912, 4 of which had simply come 

 down the slopes from the drier areas, while only a single one of the other 6 had been 

 present from the beginning. (Plate 21.) 



The total census of the strand of 1907 in the four main observational areas at the 

 close of the season of 1912 was thus seen to include the following: 



Atriplex canescens. Spirostachys occidentalis. Pluchea sericea. 



fasciculata. Parosela emoryi. Astragalus limatus. 



hymenelytra. Prosopis pubescens. Distichlis spicata. 



Heliotropium curassavicum. glandulosa. Suseda torreyana. 



Sesuvium sessile. Phragmites communis. Salix nigra. 



Baccharis glutinosa. Isocoma veneta var. acradenia. 



These plants fall into three groups: xerophytes capable of existence on soil with low 

 moisture-content in an atmosphere of high evaporating power; halophytes which might 

 endure a substratum the moisture of which was highly charged with saline matter; and 

 the single tree Salix, which would grow only with an abundant supply of water with not 

 much dissolved material. All of these plants are native of the Salton Sink in great number 

 and the action of the lake has simply resulted in their establishment on the beaches 

 in zones or bands conditioned by the sorting of the soil-material and the proportion of 

 the water supply, and salts. 



Not any emersed area at this time had reached a condition equivalent to that in which 

 it had been before the making of the lake. The plant population at Imperial Junction 

 beach, for example, included the species from the slopes above with the addition of Pluchea 

 sericea. The Travertine Terrace had been restored so far as to give a place for Isocoma, 

 but its shelves and beach ridges were as yet widely different from those near the ancient 

 beaches near sea-level. Atriplex canescens had come in, and it appears to stay in place 

 on strands during all of the changes of which these beaches are possible. Parosela emoryi 

 was also included among the species appearing on the beaches of Obsidian Island in 1908 

 and it is a constituent of the ranks marking the old strands near the ancient sea-level in 

 which the conditions tend to extreme xerophytism. 



REOCCUPATION OF THE STRANDS OF 1908. 



The level of the Salton Lake was lowered a net total of about 58 or 59 inches in 1908, 

 and the proportion of dissolved salts rose to over 0.5 per cent, from over 0.4 per cent, during 

 the year. The actual width of the bared beaches would therefore be greater than in the 

 year 1907, in which recession went on only during about ten months and amounted to 

 about 42 inches. Calculated from the slope of 1 in 300, the emersed zone on the Imperial 



