136 THE SALTON SEA. 



The 1909 strand at the Travertine Terraces bore only 3 species late in 1910; a year 

 later the number had been increased to 8, while the closing part of the year 1912 was 

 marked by the advent of 2 more; 3 additional species were seen in February 1913. The 

 steep beaches of Obsidian Island were populated in the strand of 1909 by 6 species during 

 the first year, which two years later was reduced to 3; 5 or possibly 6 species may be 

 assigned here at the close of 1912. 



The strand of 1909 on the gently sloping beaches near Mecca appeared to be populated 

 only by Atriplex and Spirostachys. It was obvious that the ranks of the invaders were 

 being depleted on the gentler alkaline slopes and accessions were being made on the steeper 

 gravelly slopes of the Travertine Terraces and on Obsidian Island. A very important factor 

 in determining this aspect of the reoccupation of the bared areas is to be attributed to the 

 saline content of the soils. 



REOCCUPATION OF STRANDS OF 1910. 



The lowering of the level of the lake during 1910 amounted to over 59 inches, and the 

 dissolved salts amounted to about 0.6 per cent on June 1 of that year. A visit to the Impe- 

 rial Junction beach in May was made and Heliotropium, Leptochloa, Scirpus, Atriplex (two 

 species), and many young plants of Spirostachys were found near the margin of the water. 



Travertine Terraces were not inspected until September, but at that time a rank of 

 Salix and Populus was found at the upper margin of the strand, while Distichlis and Helio- 

 tropium were scattered over the shelf. In October 1911 a heavy rank of Salix had formed 

 at the upper margin, in which were seen a few Populus, while Distichlis, Scirpus olneyi, 

 Pluchea sericea, P. camphorata, Juncus, Prosopis, and Heliotropium were represented. At 

 this time the flora of the strand of 1910 on the Imperial Junction beach was composed of 

 Spirostachys, Suceda, and Heliotropium. 



The only note at Mecca in June 1912 was to the effect that Heliotropium in this emersion 

 was going under, while in October only a few straggling specimens of Spirostachys and Suceda 

 were seen, although some of this might be due to agricultural operations. (Plate 22 a.) 



A few Atriplex lentiformis and Populus may be assigned to this zone also. (Plate 23 a.) 



The strand of 1910 at Travertine Terraces bore Pluchea sericea, P. camphorata, 

 Heliotropium, Scirpus olneyi, S. paludosus, Salix, and Populus in June 1912. The last 

 two named had by this time made a dense row of young trees with a height as great as 

 15 feet. In October the rank of trees (Salix and Populus) had made additional growth 

 and included some Pluchea sericea, while Pluchea camphorata, Isocoma, Scirpus olneyi, 

 Distichlis, Heliotropium, Prosopis pubescens, and Juncus cooperi were variously distributed. 



The strand of 1910 bore only a straggling growth of Suceda and Spirostachys on Im- 

 perial Junction beach when examined in October 1912. At the same time a visit was made 

 to Obsidian Island, which had not been seen since this beach was bared, and Pluchea 

 sericea, Atriplex lentiformis, Baccharis glutinosa, Heliotropium, and Spirostachys were found. 



The advent and fate of the intruders on the areas laid bare in 1910 may be briefly 

 summarized as follows: Six species germinated on the strand at Imperial Junction beach in 

 May 1910, of which two survived when seen late in 1912. Four species had come into the 

 bare area at Travertine Terraces in September 1910, and five additional ones were seen a 

 year later. Seven species were seen in June 1912, but probably the missing two, Juncus and 

 Prosopis, were overlooked, since they were found in October. On this last date the full 

 complement of 1911 was identified, with the addition of a tenth in the form of Isocoma 



I he contrast of reduced numbers of the invaders on the alkaline gently sloping beach 

 ot Imperial Junction with the increase in the occupants of the steeper gravelly slopes of 

 iravertme Terraces is again presented, the constituency of the flora of the strand of Obsid- 

 ian Island lending support to the presumption that a similar movement must have taken 

 place there also. 



