MOVEMENTS OF VEGETATION IN THE SALTON SINE. 133 



The Imperial Junction beach in May 1910 bore Heliotropium and Sesuvium in addi- 

 tion to the four present in the previous October, the entire number being represented by 

 widely scattered individuals. 



The area at Travertine Terraces was examined in September 1910, at which time 

 Pluchea sericea, Distichlis, and Heliotropium were on the strip laid bare before midsummer 

 of 1908, while the beach of the latter half of the year contained, in addition, J uncus cooperi, 

 Pluchea sericea, Astragalus, Prosopis pubescens, P. glandulosa, and Spirostachys. In the 

 two years which had elapsed since the last visit, Bouteloua, Phragmites, Salix, and Populus 

 had dropped out, while J uncus, Pluchea, Astragalus, and Prosopis had come in, probably 

 by delayed germinations of seeds deposited by the water. 



The 1908 emersion at Mecca showed Distichlis, Spirostachys, Atriplex, Prosopis, and 

 Sumda, the invasion by which could not be assigned with certainty to any given factor 

 or agency in September 1910. 



The strand of 1908 at Travertine Terraces bore only Distichlis, Salix, Prosopis pubes- 

 cens, and P. glandulosa, in October 1911, and the loss of more than half of the initial occu- 

 pants was indicative of some heavy stresses. Similar unfavorable conditions must have 

 affected Obsidian Island also, for the emersion of 1908, which had appeared so richly 

 populated on the previous visit, bore only Cucurbita, Spirostachys, Heliotropium, and pos- 

 sibly an Atriplex. The vegetation of this strand on Imperial Junction beach included 

 only Suwda, Spirostachys, and the two species of Atriplex previously noted. 



Preliminary to the final visit made to all of the observational areas in 1912, the Traver- 

 tine Terraces were visited in June 1912. Distichlis, Cyperus, Pluchea sericea, Prosopis 

 pubescens, P. glandulosa, and Astragalus were present. Here, as in the strand of 1907, a 

 single innovation was included at the last — Cyperus, which had not appeared at this place 

 before, and for the presence of which no reasonable suggestion may be made. 



The inclusive closing observations made on all of the beaches in October 1912 were some- 

 what disturbed at Mecca by the fact that reclamation operations and agricultural utilization 

 of the land below the water level of 1907 had begun and the exact limits of the area laid bare 

 by the recession of the waters could not be made out after the removal of the landmarks. 



Conditions in the other localities were much more favorable to a general examination 

 of the behavior of the plants on the strands. The emersion of 1908 at Travertine Terraces 

 bore abundant mats of Distichlis spicata, Juncus cooperi, Pluchea sericea, Prosopis pubes- 

 cens, P. glandulosa, and Astragalus. The moist condition of the soil which had persisted 

 in small spots indicated (see pp. 124, 139, and 140) a hemmed underflow. A brief visit 

 to the place was made in February 1913, at which time Isocoma, Phragmites, Heliotropium, 

 and Parosela emoryi were found, in addition to the above-named species. 



No plants could be definitely assigned to this strand on Obsidian Island; it will be 

 recalled that the vegetation was very sparse on the last visit, but Atriplex lentiformis, 

 A. hymenelytra, Spirostachys, and Suwda were probably within the limits uncovered by 

 the recession of this year. 



The strand of 1908 at Imperial Junction beach appeared to be almost bare when 

 visited in October 1912, but in two traverses three individuals of Pluchea sericea were 

 seen, the only other vegetation being a few scattered examples of Suceda. 



The surviving invaders in the strand of 1908 are thus seen to number far less both 

 as to species and individuals than the emersion of the year before, one having had six 

 years of desiccation and the other five. 



A satisfactory analysis of the movements of vegetation on the emersion of 1908 is 

 not easily to be made. The gently sloping alkaline surfaces of Imperial Junction beach 

 showed nothing during 1908, 1909, 1910, and 1911 but Atriplex (two species), Suwda, 

 Spirostachys, with an intrusion of Heliotropium in 1910 (which was not found in the fol- 

 lowing year) and of Pluchea sericea in 1912. 



