12 The Philippine Journal of Science 1923 



which the absolute dominance of the dipterocarps in the typical 

 primary forests of Malaysia is brought out, we may now take 

 up the significance of the dipterocarp distribution in the Malay 

 Archipelago. 



We have already noted (p. 3) that the two rich areas are 

 the Eastern Peninsula, with eleven genera and one hundred 

 thirty-five species, and the Sunda Islands, with eleven genera 

 and one hundred forty-four species, while the Philippines stands 

 third, with nine genera and fifty species. Why do we not find 

 the family strongly developed in the islands south of the Phil- 

 ippines and east of the Macassar Strait between Borneo and 

 Celebes, or Wallace's Line? It has been noted above that in this 

 vast region only fourteen species in four genera are known. 

 Had there been a continental area extending from Sumatra to 

 New Guinea at any time while the Dipterocarpaceae was develop- 

 ing its geographic distribution, we should certainly expect to 

 find approximately as many dipterocarps in eastern Malaysia as 

 we do in western Malaysia, or at least as many as in the Phil- 

 ippines. In the entire region from Celebes to New Guinea 

 climatic and other factors are approximately the same as in 

 western Malaysia; in other words, the entire region is essen- 

 tially adapted to the requirements of the Dipterocarpaceae. 

 Celebes is also infinitely closer to Borneo geographically than is 

 the main part of the Philippine group. 



In past geologic times much of the area between southeastern 

 Asia and Australia has been occupied by epeiric seas. Dr. Roy 

 E. Dickerson calls my attention to the facts that Java, Sumatra, 

 and Borneo are in large part covered by marine Tertiary sedi- 

 ments and that New Guinea is also largely composed of similar 

 sediments; the sediments in British New Guinea are largely 

 Miocene. The islands of Java, Sumatra, and Borneo on the one 

 hand, and New Guinea on the other hand, are land masses asso- 

 ciated with shelf seas which have consequently during Tertiary 

 times been alternately dry and flooded by shallow seas. Practi- 

 cally throughout the Tertiary New Guinea, Celebes, Borneo 

 Java and Sumatra have changed their patterns from epoch to 

 epoch. During the Pleistocene Java, Sumatra, and Borneo were 

 alternately connected and disconnected with the Asiatic main 

 land, and New Guinea was alternately connected and discon- 

 nected with Australia. Formosa has had the same history in 

 reference to Asia. The great difference between the regions now 

 delimited by the Asiatic and Australian continental shelves and 

 the intermediate insular area (the stress area between these two 



