4i6 William Russel Dudley 



Australian shores, (inc. i Malayan form), 15 species. 

 [Eight of the above extend westwardly along the 

 Indian Ocean shores to the Red Sea and down the 

 E. African coabt region, where appears one addi- 

 tional species ] 



The Antilles, (including Key West), ... 5 species. 



Pacific North America 3 



The Mediterranean,* 2 " 



Not attempting here to account for the discontinuousness of 

 these areas, we call attention to the fact that the principal cen- 

 ter named, — Australia, — is a region where an unusuallj' large 

 number of the Eocene types of land plants are found living, 

 preserved no doubt through absence of violent change in con- 

 ditions. Similarly a conspicuous number of Miocene and 

 Pleiocene forms are represented in the present Western North 

 America Flora. These facts in a broad way may have their 

 significance ; and, as bearing upon the question, we may be 

 allowed to refer, — m connection with the present uniform 

 aerial temperature of California, accompanied by a surface ma- 

 rine temperature which does not vary 10° in the year at the 

 Golden Gate,t — to the universally accepted belief that a uni- 

 form sub-tropical or warm, temperate climate existed around 

 the whole North Temperate and a portion of the Arctic zones 

 through long periods of the Tertiary, especially of the 

 Eocene and the Miocene, times contemporary with supposed 

 geologic remains of the earlj' Zosterse. 



But while the old races have been continued on this coast, 

 there have been causes at work which have brought about the 

 vigorous and remarkable divergence seen in the yarj-ing forms 

 of our genus and in the robust open-water Zostera of the Pa- 

 cific coast. This coast is geologically new. Dana asserts that 

 the Sierras were lifted in the middle of the Mesozoic, preceding 

 the Cretaceous, experiencing great subsequent elevation ; also 

 that the coast ranges date their emergence from various peri- 



* This table is constructed from stations vouched for iu Aschersou's 

 various papers, and slightly modified by later information. 



t According to Professor Davidson's observations on marine tempera- 

 tures, 1874 to 1883. 



