8 The Philippine Journal of Science 1923 



one, then, familiar with the dipterocarps as they occur in nature, 

 with the habitat complex of most or all species, with their seed 

 and seedling characters, and especially with their peculiarly 

 short-lived seeds, it becomes perfectly evident that, in order to 

 explain their present geographic distribution, it is absolutely 

 necessary to postulate previous land connections from India to 

 New Guinea over which, at some time in geologic history, it has 

 been possible for certain species to march unimpeded. 



From the geologic history of the Philippines we know that its 

 present fauna and flora, or their ancestors, originated outside 

 of the present-day limits of the Archipelago; no geologic for- 

 mation earlier than the Jurassic is known from the Archipelago. 

 From the very nature of the Dipterocarpaceae they must have 

 originated in a forested region; therefore, the Philippines must 

 have been a forested region before the dipterocarps arrived. 

 The rate of dissemination of the dipterocarps is relatively slow, 

 so that a long period must have elapsed during which land 

 connection existed between the Philippines and western Malay- 

 sia, over which the trees migrated. From the adaptability of 

 these trees to primary forest conditions (soil, humidity, rain- 

 fall, and temperature conditions practically wherever they occur 

 with us being favorable to their development) they have become 

 dominant. 



Dipterocarp forests are tall, characteristically low-altitude, 

 tropical ones of India and Malaysia, and usually occupy localities 

 most favorable to tree growth. They occur on all types of 

 topography, but are usually best developed on well-watered and 

 well-dramed plains and on the lower gentle slopes of the main 

 mountain masses. They thrive best perhaps in the humid local- 

 ities of Malaysia, where dampness and humidity are always so 



nl.^i fr S \ fi fc?. are Unkn ° Wn; yet in some r ^ ons > »«ch 

 as Bengal, the sal (Shorea robusta Gaertn. f.) thrives in local- 

 ities where the dry season is so pronounced that fires cause con- 

 siderable damage to the forests. While most of the species are 

 very strictly tropical and, in the Tropics, low-altitude forms, the 

 sal occurs in some parts of Bengal where it is injured by frost 

 < The dipterocarp forests of the Philippines reach their max- 

 imum development below an altitude of 700 meters, and ordi- 

 narily few species are found at or above an altitude of 800 

 meters. In Luzon and the central Philippines the onlv snecies 



B.ume ed S IZ 3ltitUd f ° f 80 ° m6terS ™ *-i" 

 Blume and Shorea polyspermia Merr., and we have no records 



