D. T. MacDougal—The Saltan Sea. 245 



near the extreme northwestern end of the Sink, only a few 

 feet below sea-level, show an average of 2*74 inches per year. 



10. Rapid recession of the water would result in separating 

 stranded seeds quickly from the margin of the water with con- 

 sequent rapid desiccation of the surface layer of soil, which 

 would be unfavorable to germination and survival. 



11. The shallow water lying on wide mud flats fringing the 

 shores was raised to a much higher temperature (15° to 20° F.) 

 than the body of the lake during even the winter season, 

 thereby greatly increasing its toxicity for seeds, plantlets, and 

 propagating bodies. The greater number of the seeds falling 

 into the lake would be subjected to this action. The muddy 

 flats fringing the shores at all stages of the lake must, there- 

 fore, be considered as a barrier of some magnitude which 

 would be crossed by a plant carried out into the lake and again 

 when deposited on a beach. 



Practically all of the species inhabiting the Cahuilla Basin, 

 including those native to the alpine slopes of the San Jacinto 

 Mountains, are to be included among the forms, the seeds 

 of which might be carried by run-ofl streams, winds or other 

 agencies down to the unoccupied areas around the receding 

 lake. The differences in climatic conditions and in the soil, 

 however, would obviously constitute an effectual barrier to 

 the greater number of the plants native to the rocky slopes 

 of the mountains. Some of the barriers affecting the dispersal 

 of species on mountain slopes are much too subtle to be 

 detected by available methods of geographic survey. This is 

 well illustrated by the cultures made at the Desert Laboratory, 

 in which many species abundant on the higher slopes of 

 the Santa Catalina Mountains in positions from which 

 their seeds must have been carried to the lowlands in myriads 

 for centuries, are not found below a certain limit, although 

 when the seeds are transported by man to the lower lands the 

 plantlets survive and in some instances, such as that of Juglans, 

 outstrip the lowland species in growth-activity. 



The species inhabiting the bajadas or detrital slopes of the 

 basin, or of the lowermost part of it included in the Salton 

 Sink, would be the most important elements in any invasion of 

 surfaces left bare by the receding waters of the lake. 



A number of introduced species and weeds would constitute 

 another element, and plants of this kind would be carried 

 along the line of the Southern Pacific Railroad, which runs at 

 varying distances from the shore of the lake for about three- 

 fourths of its length. The water actually washed the ends 

 of the ties for many miles of the line at the maximum level. 

 It will be recalled also that a long stretch of the track 

 previously ran below the maximum level and was moved up 

 the slope to evade the rising waters. 



