23, i Merrill: Distribution of Dipterocarpaceae 7 



limiting factor. Brandis 6 has called attention to the fact that 

 not only are various species gregarious or semigregarious, but 

 the sal, Shorea robusta Gaertn. f., stands much shade when 

 young. Brown 7 verifies this observation in the case of the 

 Philippine Parashorea malaanonan (Blanco) Merr.; his data 

 and graph showing the rates of growth indicate clearly that 

 Parashorea withstands a greatly prolonged suppression period. 

 This is especially true of the seedling and sapling stages where 

 the start is made in the virgin forest. Brown shows that the 

 suppression period is so great in the primary forest that as 

 much as seventy years may elapse before the trunk attains a 

 diameter of 5 centimeters, although the rate of growth after this 

 long suppression period is very rapid. It would seem that all 

 or most dipterocarps have this adaptability to a long supres- 

 sion period in early life; hence their ability to thrive in and 

 eventually to dominate the dense primary forests of India and 

 Malaysia. 



Most dipterocarps have winged fruits, yet they are definitely 

 not adapted to wide dissemination by wind. The fruits are in 

 general too heavy for wind distribution, while the wings are 

 adapted to provide a gyratory motion in falling, rather than for 

 horizontal distribution. Except in the genera Vatica and Isopt- 

 era, the seeds or fruits do not present the slightest adaptation 

 for dissemination by water. Burkill 8 briefly discusses the adap- 

 tation of the fruits of Vatica ivallichii Dyer and Isoptera borneen- 

 sis Scheffer for dissemination by water. He finds that the fruit 

 of the former floats for an average period of twenty-two days, 

 while that of the latter, deprived of its corky sepals, sinks 

 within a period of sixty hours. He states that it is not possible 

 to regard water distribution as in any way ancestral in the order. 

 Generally speaking, the seeds of the dipterocarps are noted for 

 their brief period of viability; they do not in general withstand 

 drying out, which is perhaps one very potent reason for their 

 practical nonoccurrence in open places. The trees from seed 

 and seedling stages to full maturity are clearly adapted to the 

 shade, temperature, moisture, and light conditions characteristic 

 of the dense tropical primary forests of India and Malaysia. To 



"Brandis, D., Journ. Linn. Soc. Bot. 31 (1895) 6. 



T Brown, W. H., Vegetation of Philippine Mountains, Bur. Sci. Publ. 

 13 (1919) 157, fig. 2. 



•Journ. Straits Branch Roy. Asiatic Soc. 86 (1922) 276, 281. 



