118 Botany 



repletion may or may not be accompanied by irreversible growth alterations. The 

 osmotic activity of the sap and its content of mineral salts and organic matter are 

 increased with a lowered water-balance, but the acidity remains practically un- 

 changed. Succulents are regarded as representing the highest type of specializa- 

 tion under arid conditions. A speculative consideration is given to the origination 

 and evolutionary development of these forms. 



No. 129. MACDOUGAL, D. T., and W. A. CANNON. The Conditions of Parasitism 

 in Plants. Octavo, in+60 pages, 10 plates, 2 text figures. Published 

 1910. Price $1.00. 



A description is given of the newly discovered parasitism of Krameria can- 

 escens and K. parvifolia, with details of the relations of the parasite to its prin- 

 cipal hosts. The more important features of structure and the results of some 

 experimental tests of the action of the parasite are set out. Cannon adds a tenth 

 family of plants to the list of parasites among the higher plants. The results of 

 an experimental analysis of parasitism are given. Regenerated cuttings of a num- 

 ber of desert plants were inserted in the bodies of cacti and other succulents, upon 

 which many were successfully grown as xeno-parasites. Chemical analysis of the 

 sap of the plants reveals the fact that a higher osmotic activity is necessary to 

 enable one form to become parasitic upon another, but the actual assumption of 

 dependent relations may be prevented by many things, such as excretions and vig- 

 orous formation of scar-tissue. 



No. 193. MACDOUGAL, D. T., and COLLABORATORS. The Salton Sea: A Study of 

 the Geography, the Geology, the Floristics, and the Ecology of a Des- 

 ert Basin. Quarto, xi-f-182 pages, 32 plates, 4 figures. Published 1914. 

 Price $5.00. 



The geological and biological processes of the surface layers of the earth's crust 

 are profoundly different under subserial exposures to those which prevail under 

 subaqueous conditions. Any region, therefore, which may be subjected to sub- 

 mergence and to weathering, alternately, will offer a changing complex of envi- 

 ronic conditions, with accompanying disturbances in the balance and distributional 

 movements of the organisms of the region. 



The great Cahuilla Basin, which lies to the westward of the lower or southern 

 part of the main stream of the Colorado River has been the scene of alternation of 

 the kind in question. The lower part of this basin has been submerged and desic- 

 cated many times in the last few hundred years, as attested by the numerous beach 

 or strand formations and layers of travertine on the shores. The making of the 

 lake in 1904, 1905, and 1906 at the time of the organization of the work of the 

 Desert Laboratory, offered opportunities for some studies the results of which 

 are presented in the present paper. The facts to be considered were so diverse in 

 character, and the necessary methods of calibration and estimation so unlike, that 

 the co-operation of a number of workers in various branches of science was enlisted. 



A general sketch of the geology and topography of the basin was furnished by 

 the late Prof. W. P. Blake, whose barometric measurements as a member of the 

 Williamson expedition in 1853 first established the fact that the region was an 

 inclosed basin, the lowermost part of which was below sea-level. The history of 

 earlier travel and the general geography of the basin is described by Mr. G. Sykes, 

 geographer of the Desert Laboratory. The analyses of water samples have been 

 carried out under the direction of Prof. R. H. Forbes, at the Agricultural Experi- 

 ment Station of Arizona, by the aid of Dr. W. H. Ross and Prof. A. E. Vinson. 

 The surface geology, with especial reference to the soil formations, has been the 

 subject of careful examination by Mr. E. E. Free, formerly of the United States 

 Bureau of Soils. Prof. G. J. Pierce, of Stanford University, has contributed the 

 results of studies of organisms living in brackish and saline waters, which are of 

 especial concern with the subject, particularly in the stages of the desiccation of the 

 lake yet to come. Prof. M. A. Brannon, of the University of North Dakota, has 

 carried on a series of cultures by which the specific action of micro-organisms to 



