MOVEMENTS OF VEGETATION IN THE SALTON SINK. 171 



had disappeared, while Scirpus, with a seed especially liable to be carried by the currents, 

 had come in. An additional island had been laid bare a short distance north of Big Island 

 some time during 1909, and in October of that year the restricted bit of gravel and sand 

 which might offer conditions for plants bore a few individuals of Pluchea camphorata and 

 Sesuvium, both of which might have been wind-borne, though Sesuvium may have come 

 by any of the methods mentioned above. Although the lake abounded in fish and these 

 were used as food by the birds, no direct evidence was obtained that they were effective, 

 directly or indirectly, in the transportation of seeds. 



The next inspection of the surface of these islands was made in October 1912, at which 

 time all had become connected with the main part of Big Island. The slopes of this bore 

 only Atriplex fasciculata, Suceda, and Eriogonum deserticola, not identical with the pioneers 

 on the beaches of the lower lands. The northernmost islet now bore Spirostachys and 

 Heliotropium on a clayey flat, while Atriplex leniiformis, Pluchea sericea, and Baccharis 

 glutinosa were on the higher rockier ridge. The original introductions had thus disappeared 

 and the later flora was like the pioneers in not being derived from the slopes of Big Island, 

 but was composed of species which were probably wind-borne, or had come from seeds or 

 plantlets deposited by the waves, while birds may have been responsible for some; all had 

 crossed a water barrier at least 10 miles in width. 



The lower areas in this archipelago were much frequented by aquatic birds, while on 

 all of the visits tracks of a number of small quadrupeds were seen. On the final visit in 

 October 1912, the tracks of a raccoon were seen; burrows of rodents were numerous; the 

 round foot-prints of some member of the cat family were in evidence, and small lizards 

 abounded. No estimate could be made of the numbers of any of these animals. Two 

 rabbits were seen, however; these and the rodents feed upon plants and seeds and their 

 activity may have had a very direct connection with the disappearance of the species 

 noted above. This island has been continuously isolated since some time in 1904 or 1905, 

 a matter of some importance in the heredity of these short-lived species. 



In October 1912 a small rocky island, separated from the western shore of the lake 

 by a stretch of open water 500 feet in width, was encountered near the Carrizo District. 

 Some clayey silt was found among the rocks. Spirostachys was represented by several 

 young plants and two individuals of Heliotropium in bloom were seen. The rocks and 

 clay near the margin of the water were coated with a blue-green alga. Some of the Spiro- 

 stachys grew up beside a cormorant's nest and may well have been brought there by these 

 birds, although this species is such a ubiquitous invader that its movements can not be 

 ascribed entirely to any one agency. (Plate 32 b.) A shoal with a clayey and sandy surface, 

 lying a few yards off the shore at the extreme southwestern corner of the lake, was inspected 

 on the following day and bore only Spirostachys and Suwda. (Plate 32 a.) 



