Malaysian Phytogeography and Polynesian Flora 257 



Islands), Calogyne (China), Osbornia (Borneo), Didiscus (Bor- 

 neo), and Strophioblachia (Indo-China). No representative of 

 any of these genera reaches Formosa, yet most of them extend 

 to northern Luzon and some even into the Batan and Babuyan 

 Islands, between Luzon and Formosa. 



In general, the eastern Malaysian types have not extended 

 north of the Philippines, and their western migration also stop- 

 ped there, as the eastern migration of many western Malaysian 

 types ceased in Borneo, the Palawan-Calamian group in the 

 Philippines, and the Philippines proper. 



This is entirely in accord with the supposed geologic history 

 of the Malaysian region. The constantly insular area in the un- 

 stable region lying between the Lombok Passage and Macassar 

 Strait, extending north along the western boundary of the Philip- 

 pines to the west and east to the islands off the western end of 

 New Guinea, including the Lesser Sunda Islands, Celebes, the 

 Moluccas, Gilolo, and all the Philippines except the Palawan- 

 Calamian group, effectively inhibited a general east and west 

 migration across this region, not only in the Recent and the 

 Pleistocene, but also during the Pliocene and probably some of 

 the Tertiary. Undoubtedly there was some late east and west dis- 

 tribution across the southern part of this unstable insular area 

 but, in general, the routes of migration seem to have been north- 

 east from Sumatra, Java, and Borneo into the Philippines, and 

 thence south and southeast to Celebes, Gilolo, and New Guinea, 

 and vice versa. The species that succeeded in extending their 

 ranges apparendy were forced to travel along the two longer 

 sides of a triangle, its base approximately in the position of the 

 Lesser Sunda Islands and its apex somewhere in Luzon. 



When a genus is described from material collected in a certain 

 place and is known only from that region for many years, we 



