22,3 Reyes: Woods of the Philippine Dipterocarps 297 



functions in the economy of the plant; namely, conduction and 

 mechanical support. On the other hand, parenchyma cells are 

 thinner walled and less attenuated (often rectangular in section) 

 and exhibit simple pits. While the walls often respond to 

 lignin reactions, they are seldom as strongly lignified as those 

 of the prosenchyma. The parenchyma cells of wood act as 

 storage organs and function as long as they are a part of the 

 sapwood; in addition, those composing the wood rays likewise 

 are concerned in radial conduction. 



The prosenchymatous tissue of Parashorea consists of vessels 

 (trachea?, pores, ducts), tracheids, and libriform fibers and 

 extends vertically (longitudinally) in the wood. The parenchy- 

 matous tissue on the other hand consists, in part, of cells that have 

 their long axes arranged vertically, the so-called vertical paren- 

 chyma, and in part of ray parenchyma which makes up the 

 wood rays. Either type may give rise to idioblasts through 

 intracell formation of crystals. In addition, the epithelial cells 

 surrounding the resin cavities must be considered in the light 

 of parenchyma, but whether they are of the same origin as the 

 vertical parenchyma cells is open to argument, as in the case of 

 the conifers. 



Vessels (tracheze, ducts, pores).— (Plate 2, fig. 8.) The ves- 

 sel segments are of a prosenchymatous nature and are the most 

 conspicuous elements in macerated material owing to their large 

 size. They appear as cylindrical structures with "tailed" ends, 

 which taper abruptly from alternate corners, and vary in diam- 

 eter and length, respectively, from 108 to 317 ? (average, 236) 

 and 147 to 550 p (average, 465). As in other woods their 

 width is in inverse proportion to their length. A round per- 

 foration, opening out from either end, indicates the original 

 interdependence of the segments as they occurred in vertical 

 rows in the wood. 



The walls of the vessel segments are comparatively thin, 

 measuring from 3.6 to 7 fi in thickness, and are marked with 

 bordered or semibordered pits, which conform to three types 

 and owe their orientation to cells contiguous to the segment. 

 Where tracheids abut on the radial or tangential walls, vertical 

 or twisted bands of small, typically bordered pits result. The 

 larger pits with vertical grouping, which at first glance appear 

 to be simple but are in reality semibordered, indicate the posi- 

 tion of vertical parenchyma cells which are coterminous to the 



