56 CARNEGIE INSTITUTION OF WASHINGTON. 



protoplast were included in the starvation phenomena. Some star- 

 vation effects remain after several years of restored normal conditions. 



The reduction of transpiration or water-loss in desert plants is not 

 one of maximum rate, but consists in a check or lessening of the rate 

 earlier in the day than in other plants. 



The densities of the sap of desert plants are lowest in species native 

 to arroyos and ascend in a scale through those of cafions, rocky slopes, 

 and bajadas to the highest values in sahne areas. 



The successions of plants which occupy an area originally bare finally 

 reach a climax formation the nature and permanence of which are deter- 

 mined by climatic control. Four great vegetation eras, viz, Eophytic, 

 Palseophytic, Mesophytic, and Cenophytic, can be recognized in the 

 history of terrestrial vegetation. 



The chief physical factors and their determinative effect upon vege- 

 tation at various altitudes from a low desert to the top of an insular 

 mountain have been evaluated. 



The field work necessary to a complete survey of the Cactacese has 

 been brought to an advanced stage by expeditions to the West Indies, 

 Brazil, and Argentina. 



The Salton Sea receded about 50 inches during the year ending July 

 1, 1915, an amount in excess of that of the previous year. The total 

 recession now amounts to nearly 40 feet or nearly one-half the original 

 maximum depth. The total dissolved salts has increased from 0.32 

 per cent in 1907 to 1.37 per cent in 1915. The heightened salinity of 

 the w^ater has been followed by changes in the revegetation of the 

 beaches and by the cessation of deposition of calcium carbonate on fixed 

 objects near the surface. This implies changes in the marine as well as 

 in strand organisms. 



Preliminary examination of the playas, bajadas, streamways, lake 

 beds, faults, and terraces of the Mohave Desert region has disclosed 

 evidences of chmatic variation and of movements of the surface which 

 it is hoped may be interpreted to account for the origination, phylogeny, 

 and successions of the vegetation which now characterize the region. 



The desert rubber plant {Parthenium argentaimn) under domestica- 

 tion has been found to show over 100 strains separable by habit, struc- 

 ture, form, and rubber content. 



The studies of the role of the factors in a desert complex prove that 

 the more divergent part of a population is eliminated by environic 

 agencies, but this eliminating action is subject to various modifications. 



The mutating stocks of beetles have continued to produce mutants 

 as in previous years, one being an additional or second departure from 

 the original. Another type of modification, consisting in alterations 

 of the stripes on the elytra of beetles, which was first apparent as a 

 small variation or departure, shows an orthogenetic progression, the 

 new characters being genetically stable. 



