164 



THE SALTON SEA. 



nation at once. Prosopis pubescens and P. glandulosa sink at once and the seeds of the 

 first begin to germinate within a few days. Scirpus paludosus had a large number oi seeds 

 afloat after 120 days, although more than half had sunk while a few had germinated^ Seeds 

 of Suceda behave much like those of Scirpus, except that a greater proportion sink within 

 a day or two and germination ensues more quickly among these at the bottom, beginning 

 within two or three days. It is thus seen that 9 of the 15 species tested ^ remain afloat for 

 a length of time which would permit them to be driven by the action of the waves a dis- 

 tance equal to the long axis of the Salton Lake. It is evident, however, that a consideration 

 of the flotation of the seed alone affords evidence of but little conclusive value m the study 

 of the revegetation of a sterilized area such as that under discussion. The fate of the seed 

 at the end of its flotation period or of the seedling is quite an important consideration. 



The results of floating seedlings has probably not hitherto had adequate evaluation 

 as a bio-geographical factor in dissemination and dispersal. The evidence of the flotation 

 tests makes it plain that in 10 of the 15 species tested the flotation period of the seed, 

 which in the different species may be from a day or two to four months or more, may be 

 followed by the survival of the plantlet for periods of such length as to render them liable 

 to be carried about by many agencies. 



Buoyant plantlets may remain on the surface or in the surface layers of the water 

 for a period as great or in some cases much greater than that of the seed, and their sur- 

 vival would depend upon the nature of the beaches on which they might become stranded. 

 The successful tests with Sesurium, Leptochloa, Pluchea, Spirostachys, Prosopis, and others 

 showed that plantlets which had floated for two or three weeks were sound and healthy 

 and sent roots down into the substratum when "stranded," in imitation of their probable 

 action in the lake. Plantlets of Rumex remained sound and made a slow growth after 

 a flotation period of two months, but their stranding test was made with soil saturated 

 with the Salton water of 1912, in which they have not survived around the lake. The 

 latest introductions of the species on the beaches was upon soils saturated with water of 

 the concentration of 1908, which had but little more than one-third of the salt-content 

 of that of 1912, but it came on the Imperial Junction beach again in 1911, when the alkaline 

 soil was being overlaid with silt from the Alamo inflow. There is but little in this behavior 

 to suggest special adaptation or peculiar fitness, since the seedlings of almost any land 

 plant will float, especially in the sunlight with the copious liberation of free gases. 



Writers on plant-dispersal have been disposed to regard ready germination as preju- 

 dicial to wide dissemination, although it is admitted by Guppy that the species included 

 in the mangrove formations are widely distributed by the action of currents. 1 Some of 

 the species encountered about the Salton present the condition of the radius of possible 

 dissemination being greatly lengthened by flotation of seedlings. 



Another phase of the movement of seeds and propagative bodies into the sterilized 

 areas of the beaches peripheral to the lake is that by which the ephemeral run-off streams 

 following rainstorms carry material down the slopes, effecting a radial penetration and 

 arrangement of the introduced species. Some slight action of this kind was observed on 

 Obsidian Island, where one or two species were carried down from the summits which rose 

 above the water even at its recent highest level, but it was most marked on the western 

 shore of the lake, where long bajadas come down to the lake from the mountains several 

 miles distant, and similar action was also indicated by some of the movements of vegetation 

 at Mecca. 



The actual weight or size of the seed or body would have but little influence, since 

 the force of these streams which may run in any given "dry" channel but a few hours in 

 a year is such that the finest sand and rocks weighing several pounds are tumbled along 



•Guppy. Observations of a naturalist in the Pacific, vol. ii, pp. 76-87, 1906. See Chapter IX, "Abortive germina- 

 tion in warm seas." 



