MOVEMENTS OF VEGETATION IN THE SALTON SINK. 159 



places around the lake, although it is not known how many plants arose in this way. It 

 is certain, however, that the duration of such individuals would be brief unless they were 

 near a spring or seepage. Typha has appeared in the emersions of 1911 and 1912 near 

 Mecca, but here the ground is high in moisture and numerous seepages and overflow 

 channels from Wells make conditions widely different from those at the lower end of a 

 desert bajada. Numerous colonies of mature plants fruiting abundantly are also present 

 up the slopes from the Mecca location, so that its dissemination here may be considered 

 simply as a spreading down a slope already occupied by it. The seeds are known to sink 

 within a very short time after they fall upon the water and almost all cases of their dispersal 

 must be attributed to air-currents. 



Wislizenia refrada was seen but once and then on the emersion of 1907 on the western 

 side of the lake, along with Franseria, Hilaria, and other species of arid habitats. It 

 played no further known part in the initial occupation of the beaches. 



THE MOVEMENTS OF PLANTS INTO STERILIZED AREAS. 



The main thesis of this paper has been that of the manner in which seed-plants were 

 carried into moist zones or strands around a receding lake which had been completely 

 sterilized by immersion in the salt water. The submerged area of nearly 500 square miles 

 was part of an extremely arid region, the native flora of which is fairly represented by the 

 census of the Sink above the present water-level. The number of species is small and 

 includes 8 trees, 23 shrubs, 10 semi-shrubs, 30 perennial herbs, and 51 annual herbs. These 

 plants being present on the slopes of the Sink, their seeds would be most liable of all plants 

 to be carried down to the beaches. The agricultural operations on the slopes to the south- 

 ward of the body of the lake brought into this region 31 additional species, which were 

 also especially liable to be carried to the bared areas. Besides those included in the pre- 

 ceding number, every species within a long radius to the southward and eastward might 

 be considered as being liable to be carried to the strands of the receding lake. The high 

 mountain wall to the westward would form a fairly effectual barrier in that quarter. 



The culture ground or emersed strips to which attention was directed were not in a 

 static condition, however. The ground was arid and the soil variously charged with salts 

 varying in composition and concentration. The observations of Mr. E. E. Free, recorded 

 in this paper, show that the soluble content of the soils was not materially modified to 

 any great depth in places which have been laid bare by the receding waters during the first 

 six years' recession of the lake. The moment that the waves failed permanently to lave 

 any part of the strand, therefore, it began to pass from a saturated condition back to the 

 desiccated state induced by the arid climate of the region. The surface layer, a few inches 

 in depth, would at first contain a soil-solution approximately equivalent to the water in 

 the lake, but evaporation rapidly concentrated this, and the plant which might have found 

 a foothold in the comparatively fresh soil would be subjected to the action of solutions of 

 increasing concentration. The salts dissolved in the water of the lake increased from 0.25 

 to nearly 1 per cent during the period of the observation, so that even the initial conditions 

 of emergence of the soil changed progressively. 



Sixty species were found on the beaches examined during the six years in which the 

 observational areas were examined closely. These beaches amounted to about 5 square 

 miles only, but since they were chosen to include diverse soils and slopes they probably 

 represent more than a majority of the species introduced. Five trees, 17 shrubby species, 

 and 38 herbaceous forms were included among those which appeared upon the beaches 

 during the period mentioned. Two of the trees inhabit moist areas, while the other three 

 are of xerophytic habit; 9 of the shrubs are halophytes and survive in soils varying in 

 salt content, this habit being most pronounced in Suceda and Spirostachys and least per- 

 haps in Bacdiaris or Pluchea. Eight of the herbaceous pioneers are halophytic, while the 



