DEPARTMENT OF BOTANICAL RESEARCH * 



D. T. MacDougal, Director. 



Definite progress may be reported in the attainment of experimental 

 results concerning environic response and physical relations of plants and 

 animals, in the determination and calibration of photosynthetic and other 

 photochemical activities of green plants, in the coordination of data which 

 establish some major conclusions as to climatological history during recent 

 time, and in the accomplishment of systematic observations v^hich yield con- 

 clusions of importance as to the origin and fate of plant population in the 

 course of such climatic alterations. The recession of Salton Lake has now 

 reached an anticipated stage in which a general summarization of its conse- 

 quences may be profitably made, and the preparation of a volume dealing 

 with the principal physical and biological phenomena disclosed by several 

 collaborators has been begun. It is gratifying to record that it has been 

 possible to put into effect and continue cooperative arrangements of sub- 

 stantial importance with research associates and workers representing many 

 different kinds of scientific effort and several institutions. 



THE SURFACE GEOLOGY AND VEGETATION OF SALTON BASIN. 



The observations upon Salton Lake and its effect upon the vegetation of 

 the basin in which it lies have noAv been carried on for six years. The origi- 

 nal maximum depth of the water of 84 feet has been reduced by an evapora- 

 tion of about 72 inches yearly. Of this theoretical total, however, amounting 

 to 310 inches, 12 feet have been replaced by inflow of precipitated water, 

 underflow from the mountain drainage, and waste from artesian wells and 

 the irrigation systems which have been developed in the southern parts of 

 the basin around the towns of Brawley, Imperial, El Centro, Holtville, 

 Heber, and Calexico. 



The recession of the margin of the lake has resulted in uncovering an area 

 of about 100 square miles. The horizontal movement has of course depended 

 directly upon the gradient. This was gentlest at the northwestern and south- 

 eastern ends of the lake, and in places the water does not come within 3 

 miles of the limits reached in 1907. 



The lowering of the level of the lake has of course not proceeded regu- 

 larly. Extended periods have been noted during which the level remained 

 fairly constant by reason of the lowered rate of evaporation and the volume 

 of the inflow. This fact, together with the seasonal action of the vegetation 

 in maturing seeds and propagative bodies, has furnished some phenomena 

 of reoccupation of exceptional interest. 



♦Situated at Tucson, Arizona. Grant No. 674. $35,680 for investigations and 

 maintenance during 191 1. (For previous reports see Year Books Nos. 2-9.) 



4— YB 49 



