142 THE SALTON SEA. 



BIOLOGICAL AND PHYSICAL CONDITIONS OF DISSEMINATION AND REOCCUPATION. 



The sterilization of an area of land surface and its exposure to invasion of plants and 

 animals start a series of distributional activities which may not come to a condition of sta- 

 bility or quiescence until after an extended series of adjustments and successions have been 

 displayed. The initial rush of immigration to an unoccupied area would make visible to 

 the observer the action and relative value of the disseminating agencies which are ordinarily 

 hidden from view, demonstrate the selective action of habital complexes, and give scope 

 to any of the possibilities usually associated with the rapid multiplication of the individuals 

 in the successive generations of any lineal series. The inrush of forms into such an unoccu- 

 pied area unbalanced by the competition and resistance of resident forms would permit 

 species to exist under physical conditions near the limit of endurance and under the influ- 

 ence of environic complexes with which they do not usually come into contact. Some 

 special inductive effects expressed in the architecture or in the qualities of the biotic ele- 

 ments might be expected under such circumstances. 



The sterilization of the Salton Sink by the making of the lake and its gradual recession 

 leaving a continuously widening strip of beach or strand around the decreasing body of 

 water has given unexcelled opportunities for the determination of some of the more im- 

 portant phases of the reactions denoted above. In this instance the bared area lay in the 

 midst of one of the most arid areas in the western hemisphere. 



When the fresh waters of the Colorado River were poured into the Sink of the Salton, 

 rapidly at first and then in a diminished stream which continues through the irrigating 

 system to the present time, there is but little doubt that the seeds, rhizomes, and propa- 

 gating bodies of many hundreds, perhaps thousands, of species were carried down into the 

 lake. The vegetation which might thus contribute to the swarm of invaders comprised 

 the various types of desert plants native to the arid regions in Arizona, California, Utah, 

 Nevada, Colorado, and perhaps Wyoming, as well as the species native to the slopes of the 

 Cahuilla Basin. The total list of invaders which survived and made some occupancy of the 

 beaches includes less than 60 species, as detailed on page 141. These played most unequal 

 parts in the pioneering. Some were represented by single individuals, others by two or 

 three, while others formed dense ranks on the beaches which must have included hundreds 

 or thousands of individuals annually. 



The difference between the vegetation of the first emersion and that of succeeding 

 seasons was far greater than that indicated by the difficulties of invasion or by the toxic 

 action which might be ascribed to the simple and direct concentration of the lake water. 

 In fact, a comparison of the data obtained by the chemist (see page 39) shows that a 

 simple concentration of the lake water did not take place. Among other things the amount 

 of potassium in the water showed no increase, although the amount present was probably 

 adequate for the nutrition of all of the plants concerned. Next it was found that the mag- 

 nesium lagged behind in the increase of the elements present in the water. The most 

 striking feature of the chemical analyses, however, was illustrated by the calcium determina- 

 tion, this element soon beginning to show a marked divergence from the main course of con- 

 centration. The possible significance of this deviation may be best understood when it is 

 recalled that sodium in large proportions is toxic to plant protoplasm. This toxic action 

 does not occur in the presence of calcium when the two elements sustain certain propor- 

 tions to each other. Whether or not this masking or antagonizing effect is produced in 

 the complex solution of Salton water is not known. 1 



It is not possible to predicate with any exactness the probable compounds of the ele- 



