23,1 Merrill: Distribution of Dipterocarpaceae 21 



matched by living plants, the time element involved being several 

 hundred thousand years. The Pliocene and Pleistocene Malay- 

 sian floras were not, then, radically different from the modern 

 flora, being practically identical with that which exists to-day 

 in the primary forests of Malaysia. Great changes in the floras 

 of temperate regions are admitted for these epochs, but the 

 equatorial region of Malaysia presents almost no changes, even 

 in species. We may then consider that our present flora, that 

 is, of the forested regions, is a Pliocene and Pleistocene one that 

 has persisted with comparatively slight modifications. This in- 

 volves the assumption that there were practically no changes in 

 the general climatic conditions in the equatorial regions of Malay- 

 sia at low altitudes during the periods of great extension of the 

 ice caps in the temperate zones, and this assumption is substan- 

 tiated by the Pliocene and Pleistocene fossil marine faunas of 

 both Java and the Philippines. 



With this digression regarding the geologic history of the 

 Malaysian region, we may now return to the subject of the 

 geographic distribution of the dipterocarps and its bearing on 

 the origin of the Philippine flora. The facts regarding their 

 distribution have already been stated. The conclusion to be 

 drawn from the paucity of forms in eastern Malaysia is perfectly 

 evident. While the various forms could spread easily over the 

 continental area comprising what is now southern Asia and the 

 Sunda Islands, and to a very definite degree into the Philippines 

 over the Sulu and Palawan bridges, they could not cross the 

 narrow sea channels separating Borneo from eastern Malaysia. 

 Only a few forms succeeded in reaching Celebes, the Moluccas, 

 and New Guinea, and these by the roundabout routes over inter- 

 mittent and always narrow connecting isthmuses from Mindanao 

 to Celebes via the Sangi Islands, and to Gilolo and New Guinea 

 via either Celebes or Talaut Island. Possibly a few came from 

 Java through Bali, Lombok, and what are now the Postilion 

 and Paternoster islets to southwestern Celebes. 



In this connection it is of definite interest to examine Diels's 

 recent paper on the Dipterocarpaceae of New Guinea. 26 He 

 enumerates ten species in four genera for New Guinea ; namely, 

 Anisoptera, four; Hopea, three; Shorea, one; and Vatica, two. 

 Of these Hopea celebica Burck is otherwise known from Celebes, 

 and Vatica papuana Dyer from the Aru Islands, the others so 



Papua sien, Engl. Bot. Jahrb. 57 



