MOVEMENTS OP VEGETATION IN THE SALTON SINK. 157 



third introduction took place in the zone of 1909 at the same place on the west bay of 

 Obsidian Island, which was in such position as to receive objects from the west or north- 

 west driven down the lake by northwestern winds. An occurrence was also noted on the 

 lands emerging from the water south of Big Island. The occupations seem permanent. As 

 has been shown elsewhere, this plant is a prominent constituent of the formations on 

 ancient beaches near Travertine Point, 200 feet above the recent high level of the lake. 

 The spectacle is therefore presented of a species coming onto the moist strand and becom- 

 ing established in the moist saline soil in such manner that the intense and progressive 

 desiccation does not injure it. The only other plant which appeared in the present work 

 with a similar capacity of endurance was Franseria dumosa. (Plate 29 b.) 



Parosela spinosa attains the dimensions of a small tree along numerous washes in 

 the Sink and is especially abundant near the Travertine Terraces, but its single appearance 

 on the beaches was upon the gently sloping shores to the southward, in the emersion of 

 1908. Nothing is known as to its reactions to saline solutions and no tests were made of 

 the seeds. 



Phragmites communis is found at numerous places all through this region where springs 

 and seepages afford sufficient soil-moisture, and many thousands of rhizomes must have 

 been carried into the lake by the inflowing current. The first occurrence of these was 

 noted at the Travertine Terraces in 1908, where two were on the shelf laid bare in 1907, 

 and it also appeared on the emersion of the following year. Since that time Phragmites 

 has not appeared among the species occupying the beaches, although no cause for this 

 absence may be assigned, unless it be the increasing toxicity of the lake water. No doubt 

 exists as to its endurance of the lake water during 1907 and 1908; for an accretion mound 

 of a spring near Salton station, which had been submerged during 1907 and 1908, bore 

 rhizomes of this plant which had survived the immersion. It is possible, however, that 

 the toxic limit of concentration accentuated by the loss of calcium was reached in 1909 

 and that living plants were not carried by the lake after 1908. All of the known introduc- 

 tions were from rhizomes floating in the water. (Plate 18 a.) 



Pluchea sericea, or arrow-wood, is a shrub which reaches a height of 3 to 7 feet in the 

 Delta of the Colorado. The fruits bear copious pappus, on account of which it is readily 

 borne aloft by the winds. Maturing fruits were seen in May and consequently this plant 

 found a foothold on the strip which had been laid bare at this time and was still moist. 

 It appeared on all of the beaches except that it was more sparsely represented during 1909 

 and 1910 than at other times. Introduction appeared to be followed by establishment 

 in nearly every case. No well-attested records are at hand as to its extermination on any 

 beach, although it was recorded as missing in certain instances, perhaps by being over- 

 looked. The heavy stand on this plant on the strip laid bare on Imperial Junction beach in 

 1907 was still represented by a great number of individuals in October 1912, although it was 

 seen that many were slowly dying, presumably from the lack of moisture in the soil. The 

 actual margin of the lake had by this time receded over a mile from where they stood. 



Pluchea was also one of the first plants carried to the sterilized surfaces of the islands, 

 and its extreme buoyancy in the air renders it liable to be sown thickly everywhere. Mil- 

 lions of the fruits, like those of all of the compositaceous plants of the region, would un- 

 doubtedly fall into the water, but it can not be said whether or not these would germinate 

 there or in the moist mud at the margin when they became stranded. 



Polypogon monspeliensis was seen but once, in May 1908, when mature plants with 

 maturing seeds were found on ground recently laid bare by Imperial Junction beach. The 

 single introduction may have been by birds or by wave action. 



Populus macdougalii is found in moist locations at various places in the Cahuilla Basin 

 and some trees were below the maximum level of the water near Mecca. The water, which 

 at the time of the high level contained only about 0.25 or 0.33 per cent of salt, covered the 



