64 CARNEGIE INSTITUTION OF WASHINGTON. 



and Isocoma veneta var. acradenia. These two are also found in the 

 physiologically dry alkaline soils. In number of individuals they 

 probably equal the united total of all the other plants above the rank 

 of herbs. 



The Re-population of Sterilized Islands, by D. T. MacDougal. 

 The hills submerged in the formation of the Salton Sea reappeared 

 in the form of islands as the water subsided, leaving a soil with the 

 characters of the ancient beaches encircling the lake, but to which 

 there came only such species as might be carried by currents, winds, 

 or animals. Some species make seeds which float in saline waters 

 unchanged for long periods, and these might be carried across long 

 stretches of water and lodged on the shores. Others, by reason of 

 their small size, might be lifted and carried by the wind after the 

 manner of dust particles; others with extended surfaces presenting 

 wing effects or buoyant structures, such as the pappus of the arrow- 

 weed (Pluchea) , might also be carried by the wind. Great numbers of 

 birds frequent the shores of the lake and they must be taken into 

 account in any comprehensive consideration of the subject, yet proof 

 was not secured that any single species was carried to an island which 

 might not have reached the place by the operation of the other agen- 

 cies named. In addition to the above, which have received much 

 attention from geographers, it was found that some of the species 

 concerned in the occupation of the moist beaches have seeds which 

 sink within a few hours or a day of the time they are thrown into the 

 water. Germination ensues quickly in some and the floating seed- 

 lings were seen to be capable of endurance of flotation in the water 

 of the lake for periods of a month or more. These would of course 

 begin growth immediately when stranded. Cormorant Island, 

 separated from the shore by a strip of water 6 or 7 miles wide and 

 from a larger island by 2 miles, has been reached by but six species 

 in as many years, four of which are represented by two or three or a 

 few individuals. Pluchea and Baccharis probably reached the island 

 as wind-borne seeds; Sesuvium and Heliotropium by flotation of seeds ; 

 Atriplex by floating seedlings; and Spirostachys by birds, although 

 this, as well as Sesuvium and Heliotropium, have such small seeds that 

 they might have been lifted over the water barrier by winds. 



The Occupation of Sterilized Beaches and the Subsequent Changes, 

 by D. T. MacDougal. 



The manner and extent to which emersed strands were occupied 

 by plants was found to vary somewhat with the gradient of the slope, 

 the character of the soil, and the nature of the converging slopes. 

 Some species began growth on beaches within a few weeks after the 

 surfaces had been laid bare, while others did not find suitable condi- 

 tions until two or three years later. 



