Books and Current Literature. 123 



ice, are necessarily of post-glacial origin; while those on the edge 

 may have arisen in inter- as well as post-glacial times. 



The m.ore extended studies of Briquet on the post-glacial 

 return migrations of the Swiss floras (Trans. Swiss Soc. Nat. 

 Hist.), beginning with the last inter-glacial period, go to show 

 that during the final period of glaciation the vegetation of the 

 forested region was almost wholly driven out of Swiss territory, 

 while the alpine vegetation found six territories of refuge on the 

 north, northwest, east and south. Cn the return of the Swiss 

 floras after the last period of glaciation there were as many lines 

 of miigration as there had been territoiies of refuge. The char- 

 acteristics of the s(!veral floras along the lines of later migration 

 present data from w'hich important conclusions Uiay be drawn. 

 The flora of the Engadine, for example, is such that it can be 

 explained only by the existence of a post-glacial warm and dry 

 period, the so-called xerotherm period. 



Hochreutiner, in a recent publication of the botanical garden 

 of Geneva, gives the results of his elaborations of several collec- 

 tions of Madagascar plants. He concludes that this island has 

 received many of its plants by three successive im.n igrations, as 

 follows: 1. An ancient one of long duration from the east, 

 during which plants settled in the low region of the east coast 

 and adjacent tropical territory. 2. An African imm.igration, 

 more recent, but interrupted for a time long enough for new 

 species of close affinity and numerous varieties to arise. Many 

 plants of the high plateaus of the island are closely related to those 

 of south Africa. 3. A still more recent imr. igration continuing 

 to the present time determined by marine currents from insular 

 India. 



Yapp, in a paper in the Annals of Botany, discusses the re- 

 lation of stratification in the \egetation cf a m.arsh and evapora- 

 tion and tem.perature. It was found that the air in the m.idst of 

 the vegetation was more humid than that outside and that very 

 considerable differences in hun.idity existed between the lower 

 and up f er strata, and that the higher strata of vegetation are^ 



