18 BOOKS AND CURRENT LITERATURE 



or absent at Travertine Terraces, where Distichlis, Salix and Populus 

 were establishing themselves in numbers. 



Also numerically there was a difference: the first named locality 

 with its gentle alkaline slowly desiccating slopes presenting better 

 opportunities for germination had a greater number of pioneers than 

 Travertine Terraces. 



On the other hand very few pioneers were able to maintain them- 

 selves when the beaches were drying out. Thus, at Imperial Junction, 

 the number of species was reduced from 17 in 1907 to 5 in 1912, and 

 here no secondary introduction took place. At Travertine Terraces 

 the reduction in number of pioneers was counteracted by secondary 

 introductions of more or less xerqphytic plants. Still, nowhere had the 

 beaches reached a stable condition, equivalent to that in which they 

 had been before the making of the lake. 



Of the species appearing on the beaches about 80 per cent might 

 have been brought by wind, but only 12 per cent could only have been 

 brought by wind. Of other agencies, birds have probably played a 

 role, and some instances were found where ephemeral run-off streams 

 had carried species down from the land above. Flotation played a 

 very important part in the transportation of seeds; flotsam collected 

 at the water side gave a number of seedlings. MacDougal has tested 

 a number of seeds in the laboratory, keeping them in Salton water and 

 observing the duration of flotation and the germination. The plant- 

 lets were also "stranded" in imitation of the probable action in the 

 lake. It came out that "in 10 of the 15 species tested the flotation 

 period of the seed, which in the different species may be from a day 

 or two to four months or more, may be followed by the survival of 

 the plantlet for periods of such length as to render them liable to be 

 carried about by many agencies." Thus buoyant plantlets may remain 

 in the surface of the water for a long time and finally strike root on the 

 beach. Inferential as this reasoning is it gives us the doubtless true 

 but somewhat paradoxical conception of plant-dispersal by water in 

 desert areas. This is beautiful evidence that "the origination of qual- 

 ities or structures upon which dissemination would depend, in many 

 instances at least, has no possible connection in a causal way with the 

 agencies themselves" (quoted from MacDougal's "general discussion"). 



To this short review must be added congratulations to the authors 

 for the publication of this magnificent volume, pleasing by its fine 

 appearance, by its many beautiful plates, and attractive on account 

 of the great interest attaching to the subject, the systematic manner 



