144 THE SALTON SEA. 



streams. The run-off or surface flow resulted from the precipitation accompanying the 

 heavier storms, and when the streams were formed in this manner the water rushing down 

 the steep slopes of the bajadas undoubtedly would pick up the accumulation of seeds lying 

 in the shallow channels and carry them down into the lake, or perhaps cover some with 

 sand and silt which with the included moisture would be very favorable to germination 

 and survival. The invasions thus faciUtated would result simply in the advance of species 

 down the slopes crossing the strands at right angles, generally in places perhaps occupied 

 previous to the making of the lake. Such action was of course noticeable on the upper- 

 most beaches left bare during the first year's recession of the lake, and transportation by 

 this metliod became less and less efficient as the distance from the maximum-level shore- 

 line was left behind. 



The flotation by run-off streams becomes a more effective method for carrying plants 

 onto the bared strands, especially from the fact that no prolonged subjecting to soaking 

 would be endured. The subjection of the seeds to the brief action of the ephemeral stream 

 and its subsequent contact with the moistened sand or soil would be of a character highly 

 favorable to survival. It is evident that the soil conditions of the beaches during the first 

 year of recession were different from those offered in any following year. Briefly stated, 

 the surface layer had been leached to a slight depth by water containing the lowest pro- 

 portion of salts. Another feature favorable to the development of the comparatively heavy 

 vegetation of the emersion of the first year was the fact that the rapid rise of the lake would 

 have lifted seeds from the ground and thus at the theoretical moment when the lake was at 

 its maximum level the number of floating seeds which might be driven ashore by wind and 

 wave action was greater than at any subsequent time in the history of the lake. The toxic 

 activity of the water itself was least at the maximum level and began to increase at once. 

 As was noted in the history of the earliest strand, the dead stems of some species remain- 

 ing erect in place held aloft fruits which were not all cast off until after the waters had 

 receded. 



FLOTATION AND GERMINATION. 



Since it appeared that the greater number of the species were finally carried to the 

 emersed zones around the lake by water it was deemed important to make tests of the 

 behavior of some of the forms when placed in water taken from the lake. The conditions 

 were so specialized that it will not be profitable to review the literature of the general sub- 

 ject farther than to call attention to the chapter on dissemination of seeds in "Origin of 

 Species" and also to Guppy's more recent observations.' 



These tests would have had their maximum value if they had been begun when the 

 concentration of the water of the lake was lowest and the reactions of the seeds year by 

 year correlated with the occurrences on the beaches. The overweening importance of 

 flotation as a final means of dispersion was not evident, however, until the work was well 

 under way. A supply of Salton water was taken from the lake in October 1912 and shipped 

 to the Desert Laboratory at Tucson. The nearest analysis was that made in June 1912 

 (see page 47) and the concentration had in all probability slightly increased, so that the 

 solid matter dissolved amounted to about 0.9 per cent. 



A series of glass dishes was provided on a long table in a room with a north light. No 

 artificial heat was supphed and the range of temperature, due to the fact that the room 

 was kept closed during the first two months of experiments, was between 40° and 60° F. 

 At the close of this period all of the preparations were removed to a glass house without 

 artificial heat, where the temperature ran as low as 50° F. at night and up to 88° F. during 

 the daytime. The range of temperature and the alterations thus provided would be so 



' See Darwin, Meana of Dispersal, etc., Origin of species, pp. 324-330. Reprint of sixtli edition, New York, 1876. 

 Guppy. Observations of a naturalist in the Pacific between 1896 and 1899, vol. ii, 1906, London. 



i 



