22,3 Reyes: Woods of the Philippine Dipterocarps 311 



In transverse section at low magnifications they generally occur 

 as white dots 29 arranged in uniseriate rows which extend 

 tangentially — that is, at right angles to the wood rays — but in 

 certain species of Vatica, Anisoptera, and Dipterocarpus the 

 arrangement may become more or less diffuse through the in- 

 terruption of the lines. The radial distribution of the rows is 

 very variable. They occasionally become practically cotermin- 

 ous and a biseriate or multiseriate condition may result, while 

 in other trees, several centimeters may intervene between 

 neighboring series. In general, suppressed or slower-growing 

 trees exhibit the larger number, a condition which may be 

 traceable to restricted growth or resulting traumation. 30 



Dipterocarps, in common with other trees of the tropical and 

 temperate regions, exhibit interlocked grain, which is occasioned 

 through a change in the direction of the vertical elements at 

 different points along the radii of the log and results in zones 

 in which the fiber direction alternates. Whether these are cor- 

 related in any way with annual thickening or fluctuating growth 

 intensity is open to conjecture, but it is known that each rep- 

 resents the increment accruing from several seasons. Saw- 

 yers take advantage of this alternating grain in the conversion 

 of the timber and quarter-saw logs, not only to obtain a 

 "ribbon grain" which enhances the figure and value of the 

 wood, but also to obtain boards which exhibit the minimum 

 amount of warping. 



As is to be expected in a family of such wide distribution 

 in the Oriental Region and diversified habitat, dipterocarp 

 woods display much variation in such physical properties as 

 color, texture, and hardness, and lend themselves to multiferous 

 uses. A brief enumeration of some of the more-striking 



29 The resins contained in the ducts are in the liquid or semiliquid state 

 before the trees are felled but harden into a whitish mass upon drying. 

 In some species of Shorea (S. palosapis and S. eximia) the resins volatilize, 

 leaving the ducts quite empty; in others, like Dipterocarpus grandiflorus 

 they are viscous, slow-drying oils. Clover, Philip. Journ. Sci. 1 (1906) 191, 

 states that this viscous substance contains solid resin, water, and from 

 25 to 40 per cent of volatile oil, and believes it is a sesquiterpene or a 

 mixture of this class of substances. 



"In addition horizontal resin cysts are present in a few species, but 

 they are exceedingly minute and can only be seen at higher magnification; 

 however, Pfeiffer, loc. cit., states that some of the Javanese species exhibit 

 resin ducts that are visible to the naked eye. 



