MOVEMENTS OF VEGETATION IN THE SALTON SINK. 153 



underflow, so that a more vigorous growth was made on the ground some little distance 

 back from the recent high beach line. It is notable that although it was abundant here 

 it did not at any time come onto the beaches of Travertine Terraces, which were less than 

 a mile away, except in 1908, in which year it was also found on the shores of Obsidian 

 Island; it did not survive in either place. It formed along the shore line near the Salton 

 Slough in 1909, but has not maintained itself there. 



Suceda was growing on the higher slopes of Big Island when the lake was formed and 

 continued to survive there, yet it did not come onto the beaches of the outlying archi- 

 pelago less than a half mile to the southward, which emerged from the water in 1909 and 

 1910, although the northwest winds would be in a direction favorable for carrying them 

 to this distance. 



It would be allowable to suppose that some seeds were carried by birds, yet the greater 

 majority of the occurrences outside of the special cases noted above might be attributed 

 to the action of run-off streams which carried the seeds down the slopes to the beach, and 

 those remaining at the margin or in the shallow water germinated in the zonal form dis- 

 played in Plate 28 c. Seedlings of such origin or from fruits carried to the water of the 

 lake by any agency might endure sufficient flotation to cause them to be carried to some 

 distance, although the failure of the plant to appear on two beaches near maturing crops 

 of fruits does not support such an idea very strongly. It seems very probable that with 

 the increasing concentration of the water of the lake the species may appear on other 

 slopes not yet sufficiently saline to offer suitable habitat conditions. 



OCCURRENCE AND BEHAVIOR OF VARIOUS SPECIES ON THE BEACHES. 



Aster exilis was represented in the emersion of 1907 at Mecca by one plant which was 

 seen in May 1908. It was next seen in the corresponding zone on Obsidian Island in late 

 November 1908. It also appeared on the emersion of 1908 with A. spinosus. It played 

 no further part in the occupation of the beaches, although growing in abundance in the 

 Delta and on flooded lands along the inflowing streams. Myriads of fruits must have 

 been carried over the lake and lodged on the moist strands. The failure to germinate may 

 only be attributed to the concentration of the soil salts, although this has not been tested. 



Aster spinosus appeared on the shore of the southeast point of Obsidian Island in 

 the emersion of 1907, as was observed for the first time in May 1908. The plants were 

 in fruit when examined in November of that year. No further occurrence of the species 

 in emersed zones was reported. Its transportation to the locality mentioned was probably 

 due to birds. 



Astragalus limatus is a native of the arid slopes and bajadas in the western part of 

 the Sink and its appearance on the beaches was confined to those to which it might have 

 been carried by run-off streams. It occurred on the Travertine Terraces on the emersions 

 of 1907, 1908, 1909, where it has maintained itself. The first appearance of the plant in 

 any place was not on soil that had been bared less than a year. Several clumps of the 

 plant on the Travertine Terraces were observed in full bloom on February 8, 1913. 



Atriplex canescens forms a small shrub about 3 feet in height and is very abundant 

 in the Sink. It is therefore up the slope from almost all of the observational areas. Old 

 plants fell down with the crumbling banks upon the highest beach of Travertine Terraces, 

 although they did not survive; but seedlings arose here and upon terraces of the following 

 years. The plant was also a constituent of the first lot of plants on bared beaches at the 

 other observational areas. It is to be noted that while it came onto the moist soil within 

 a comparatively short distance of the water, it survived the progressive desiccation. In 

 this behavior it is comparable with Parosela emoryi, which comes on recently bared gravelly 

 and sandy beaches and persists throughout the changes resulting from progressive desicca- 

 tion, although in soils with a much smaller salt-content. 



