120 THE SALTON SEA. 



islands in the vicinity of Big Island in the southern part of the lake were taken into account 

 as they came into view and the character of the surfaces was noted in every case. 



During expeditions to these places once or twice yearly, collections of plants were made, 

 and notes and photographs were taken of the formations encountered. A large sample of 

 water was taken annually in June from the surface of the deepest part of the lake in order 

 to follow the changing composition of the dissolved salts, and also from other locations 

 and depths for comparison. A chemical and physical examination of the soils on the bared 

 parts of contiguous areas was made, together with every effort to determine the factors 

 cooperative in influencing the behavior of vegetation as it followed the receding lake. 



In addition to the sail-boat built in 1907, a steel-hulled power launch, built in the 

 shop of the Department at Tucson, and a small sectional steel rowboat were used in travers- 

 ing the lake. Land trips back from the lake and around its southern end were made by 

 camp wagons and field equipment. Some use was made of motors, despite the deep arroyos 

 and great stretches of soft sand encountered. A traverse from the extreme northwestern 

 part of the basin by motor to the northeastern part was made in September 1910, when 

 Messrs. Sykes and MacDougal carried a line of observation on the drainage and surface 

 conditions from the San Gorgonio Pass down to the lake at Mecca, thence by way of Dos 

 Palmas up the Chuckawalla Wash to the Chuckawalla Divide, and down eastwardly to 

 the Colorado River, a distance of 150 miles. Messrs. MacDougal and Sykes came through 

 the San Gorgonio Pass and went down the drainage of the Whitewater to the northwestern 

 end of the lake in June 1912. Here the party was joined by Professor Brannon and a 

 route was followed along the western and southwestern sides of the lake and across the 

 inflowing channel of the New River. From here a line was run to the western margin of 

 the basin and across the range by Mountain Springs to San Diego. Other trips were made 

 from time to time by the collaborators in this volume and the results of their field work 

 were made available for all those engaged in the work. 



FACTS TO BE ASCERTAINED. 



The energy of the entire staff of collaborators was concentrated in an effort to obtain 

 facts which might bear upon the more important problems presented by the receding lake, 

 which for convenience may be arranged in the following topical form : 



1. Composition and nature of the flora of the basin, with chief attention to the species inhabiting 



the Sink. 



2. Influence of the lake upon vegetation above the flood-level, either in increased humidity or 



hemmed underflow. 



3. Endurance and survival of the vegetation in the shallower marginal portions" of the flooded area. 



4. Geographical relations of the Sink, with especial consideration of the contributing drainage. 



5. Physical and chemical analyses of soils of the Sink, with comparisons between those unaffected 



by the recent submergence and those taken from the bared strands. 



6. Composition of the water of the lake as varying with its concentration. 



7. Algal and bacterial flora of the lake, and influence of these plants upon the composition of the 



water. 



8. Alterations in plant tissues induced by submergence. 



9. Reoccupation of the bared strands left by the receding lake by plants. 



10. Alterations or successions in the plant inhabitants of the strands with increasing aridity. 



11. Environic response of plants gaining a foothold on the strand and later becoming subject to 



desiccation. 



12. Pioneer occupants of sterilized islands emerging from the water as a result of lowered level. 



13. Agencies effective in carrying seeds, spores, and propagula to bared strands and isolated areas 



on islands. 



14. Introductions, or invasions of the Sink by species not hitherto native to the region. 



It need hardly be said that the evidence obtained on some parts of this comprehensive 

 program was very meager, and that some features, notably those of the animal inhabitants 



