GEOGRAPHICAL DISTRIBUTION 165 



tribution), where it was at first endemic,^ and whence it 

 gradually spread as far as it could. This is well illustrated 

 in the distribution of the Verbenaceae, one of the higher and 

 therefore more recent families of flowering plants, com- 

 prising about 75 genera and 1300 species, occurring 

 widely throughout tropical and temperate regions. Of 

 104 species belonging to various genera in the Philippines, 

 60 per cent., according to Lam,^ are apparently endemic. 

 These endemic forms have undoubtedly been derived from 

 the 39 non-endemic species, and will, in the course of time, 

 spread from the Philippines to neighboring islands and 

 thence to the mainland. About 85 per cent, of the 

 flora of Hawaii is endemic,^ and even the strand flora, 

 while cosmopolitan on the whole (the general rule for 

 coastal vegetation), is nearly 40 per cent, endemic, a 

 surprisingly high percentage. 



From the facts of geographical and geological distri- 

 bution, Wallace deduced the following law:* Every 

 species has come into existence coincident both in time and 

 space with a pre-existing closely allied species." "The law 

 here enunciated," said Wallace, "not merely explains 

 but necessitates the facts we see to exist, while the vast and 

 long-continued geological changes of the earth readily 

 account for the exceptions and apparent discrepancies 

 that here and there occur." And again, "this law agrees 



1 Endemic: found in a given region, but not elsewhere. 



2 Lam, H. J. The verbenaceae of the Malayan Archipelago. Gronin- 

 gen, 1919. 



' Including, for example, all the native Hawaiian palms, belonging to the 

 genus Priichardia. See MacCaughey, Vaughan. Bull. Torrey Bot. 

 Club, 45: 259-277. July, igi8, and Plant World 21 -.317-328. Dec.,1918. 



* Wallace, Alfred Russel. On the law which has regulated the introduc- 

 tion of new species. Annals and Mag. of Nat. Hist. 16, Ser.2 : 184-196. 

 Sept. 1855. 



