22,3 Reyes: Woods of the Philippine Dipterocarps 295 



Seasonal rings are wholly wanting in spite of the fact that 

 growth intensity in the tree is known to fluctuate appreciably 

 at different seasons. The wood is very homogeneous, of coarse 

 even texture, and distinctly cross grained. 



In cross section the vessels appear as large pores, which either 

 are solitary or exhibit a tendency to group themselves in rounded 

 clusters of three to six or string out in rows of three to fifteen 

 obliquely to the wood rays. In the main the ducts are open, but 

 occasionally tyloses are present, which occlude the vessels as 

 reddish cystlike ingrowths. The most conspicuous feature of 

 the section, however, and one which is of diagnostic value for 

 all dipterocarps, is the presence of resin cysts, which in this 

 species are filled with a white amorphous deposit and stand 

 out as white dots against the darker opaque background of 

 woody tissue. The resin cysts of Parashorea exhibit the same 

 arrangement as the traumatic resin cysts of conifers; that is, 

 they occur in single rows, which extend tangentially as arcs, 

 concentric with the growth rings. 11 The radial arrangement of 

 the rows is irregular; they occur at intervals varying from a 

 few millimeters to several centimeters. Isolated cysts are com- 

 monly present, but they are smaller and not readily discernible 

 with a hand lens. Tetragonal crystals of calcium oxalate may 

 be seen with the help of a magnifier as occasional whitish dots 

 bordering wood rays. When viewed with the naked eye, in 

 addition to the pores the wood rays may be seen as rather fine 

 reddish lines which extend radially through the wood. Their 

 color is traceable under higher magnification to infiltration 

 products contained in the ray cells. Only the larger rays are 

 discernible at this magnification; narrow rays, too small to be 

 visible, are interspersed between the larger ones. 



The remainder of the cross-sectional area is occupied by wood 

 elements too small to be discerned individually at low magnifica- 

 tion. Evidence of a division of labor is to be seen, however, 

 in that the pores are surrounded by lighter areas of tissue which 

 had at least some part in the transportation of water and solutes 

 while included in the sapwood. The darker areas, at some dis- 

 tance from the vessels, are composed of cells that perform 

 purely the mechanical function. 



In tangential section the vessels are conspicuous, owing to 

 their large size, and appear as articulated tubes, occluded in part 



" Complete rings of resin ducts are very rare in the dipterocarps, if 



