MOVEMENTS OF VEGETATION IN THE SALTON SINK. 127 



The gently sloping alkaline beach of Imperial Junction was examined on the same day 

 as Obsidian Island, and as the two places face each other across a 5-mile stretch of open 

 water the difference in results may be attributed chiefly to slope and soil characters. 



The original belt of Suceda, Atriplex fasciculata, and A. canescens had now become very 

 dense, while some Spirostachys was also present. In addition there had come from additional 

 germinations, Distichlis, Heliotropium, and Sesuvium sessile, and the entire formation was 

 showing indications of the increasing desiccation except Atriplex. Two species of this genus 

 were fruiting abundantly, and as they were already represented down the shore by numer- 

 ous seedlings they might be expected to constitute a strong element in the invasion. 



The plants in the zone of Pluchea sericea had made but a scanty growth, but some 

 were maturing and casting seeds which were being carried about by the wind. Sesuvium, 

 Spirostachys, Atriplex of the two species mentioned, and Heliotropium also grew among 

 the Pluchea, while these species were diffused over the area which lay above the Pluchea 

 and between it and the Suceda-Atriplex formation. Rumex berlandieri was also repre- 

 sented in the wash transecting the emersion of 1907, together with Typha, Oligomeris 

 glaucescens, Baccharis glutinosa, and Amaranthus palmeri. A comparison with the census 

 of February shows that Oligomeris, Baccharis, Sesuvium, and Amaranthus represent addi- 

 tions to the population, and their appearance is probably to be ascribed to the germina- 

 tion of seeds with the rising temperature on the advance of the season rather than to 

 new introductions. It is of course possible that the seeds of Baccharis may have been 

 brought in by the wind. Cucurbita seen in February could not be found and might be 

 temporarily reported as a loss. 



The difference between these two observational areas being so great, a visit was made 

 at once to the Mecca area on the following day. Pluchea camphorata, which was native 

 above the flood-level, had invaded the emersion of 1907 and was maturing fruits. Pluchea 

 sericea was also maturing seeds in the 1907 emersion. Distichlis was present in abundance. 

 Sonchus oleraceus was likewise casting a crop of seeds and Rumex was maturing seeds. 

 One plant of Conyza coulteri was present. Heliotropium had become very abundant. One 

 young plant of Aster exilis was found. Large numbers of individuals of Oenothera were 

 seen in moister areas, and Atriplex lentiformis and A. polycarpa were represented by large 

 rounded plants, which throve exceedingly in this locality. Suceda and Spirostachys, which 

 had originally occupied the area, were represented by numbers of young individuals. Oligo- 

 meris glaucescens, Chenopodium murale, and an unrecognized species had disappeared in the 

 three months since February, while it is to be seen that Pluchea camphorata and P. sericea, 

 as well as Distichlis, had advanced down the gentle slope into the sterilized area. Sonchus 

 oleraceus and Rumex had also been added to the population, although it could not be sug- 

 gested from what source. 



A complete round of the observational areas was made in November 1908. The Mecca 

 area appeared to furnish suitable conditions for Sumda, which had made an enormous 

 growth, while the two species of Atriplex mentioned above were still active. Heliotropium 

 and Spirostachys were seen as before. Pluchea sericea was represented by scattering indi- 

 viduals, but P. camphorata was not seen, although, as was demonstrated later, it was present 

 in abundance in seed form. 



The Imperial Junction beach was examined a day later than Mecca. No marked 

 change from the condition described in May was discernible, except that the stress set up 

 by continued desiccation had limited the growth of some of the species. Typha had appar- 

 ently succumbed, while Oligomeris, Distichlis, Heliotropium, Sesuvium, Rumex, Baccharis, 

 and Amaranthus could not be found in the hasty examination made in the twilight of a 

 winter day. The results of later examination, however, make it probable that the non- 

 appearance of these plants indicated a real failure to survive the summer temperature 

 and high evaporating power of the air. 



