BOOKS AND CURRENT LITERATURE 17 



Olneya. As general characteristics of the xerophytic formation Parish 

 states that shrubs and suffrutices are prevalent but only in few species, 

 the individual plants are separated by large intervals, have a condensed 

 growth and small, often early deciduous leaves. There are no succu- 

 lents at all. Induments have not been evolved to any marked degree, 

 and there are only two species with storage roots. Seedlings of the 

 desert shrubs have never been found (except of Parosela) although the 

 seeds are known to be able to germinate readily. 



In MacDougal's paper it is described how the plants move onto the 

 beaches as these are laid bare. The lake receded in 1907-1912 from 

 40 to 59 inches yearly, but the breadth of the emersed beaches varied 

 of course with the angle of their slope. This angle also determines the 

 duration of the wet stage of the newly emersed beach, steeper slopes 

 desiccating faster than gentle ones, and this condition again determines 

 the alkalinity. 



For the study of the differences of the beaches five areas were selected, 

 of which two only need be named here, viz., Imperial Junction with 

 a slope 1 in 300, and Travertine Terraces with a slope 1 in 20. The 

 latter locality had a gravelly soil in which the waves cut banks during 

 each winter when the evaporation was slight and the lake consequently 

 receded slowly. 



All the areas were often visited during the years 1908-1913, every 

 change in the conditions was noted and every plant was followed from 

 seedling to death or to perfect establishment. 



Although propagating bodies of hundreds of species must have been 

 carried into the lake by wind or water only 60 species in all appeared 

 on the beaches. Most of these were species inhabiting the lower parts 

 of the basin above water, but there was also a number of introduced 

 species and some species native to the valley of the Colorado River. 



Comparing the beaches in the same place we find a considerable 

 variation in number and composition of introductions in the different 

 years, suggesting differences in the dispersing agencies (wind) during 

 the time when seeds were ripe for dispersal. During later years 

 some species are dropping out from the pioneer class, which fact is 

 ascribed to the effect of the increasing amount of chlorine in the water 

 of the lake. 



The beaches of the different areas studied had in part different pio- 

 neers. For instance, at Imperial Junction Atriplex fasciculata, Spiro- 

 stachys, Suaeda and Scirpus paludosus were common pioneers, rare 



THE PLANT WORLD, VOL. 18, NO. 1, 1915 



