296 The Philippine Journal of Science 1923 



by reddish tylosic growths. The vessel segments, which arise 

 from separate initials in the lateral meristem, are distinct and 

 when viewed with a hand lens are seen to be clothed with smaller 

 cells of similar length, the so-called tracheids. The tracheids 

 and wood parenchyma give rise to the lighter areas about the 

 pores as seen in cross section. The wood rays appear in 

 sectional view as fine lines not over 2 millimeters in length. 



Radial sections are striking in appearance. The relatively 

 high wood rays are now seen in surface view against the back- 

 ground of other tissue and stand out as ray flecks which reflect 

 the light differently, causing the wood to be lustrous. The 

 vessels extend vertically and appear as in the tangential section. 

 Owing to the interlocking grain of the wood a "ribbon" figure 

 is produced, which is sometimes more distinct than that of 

 Swietenia mahagoni Linnaeus. This feature of the dipterocarps, 

 as previously noted, is exploited by lumbermen, who in sawing 

 their logs radially or nearly so not only obtain boards with 

 enhanced figure, but at the same time reduce possible warping 

 in seasoning to a minimum. The best ribbon effect is obtained 

 when the wood rays are cut at an angle of 10° to 25° to the 

 surface of the board. 



Two methods of procedure are open in discussing the micro- 

 scopical structure of wood. In the one case the tissue itself may 

 first be dealt with and its several anatomical features enumerated 

 at length, and following this the various elements that compose 

 the wood may be obtained by maceration and their structure 

 studied in detail. This order may often be reversed to advan- 

 tage, since the structure of wood — that is, the arrangement of 

 the cells that compose it — can best be interpreted when the 

 intimate morphological features of its individual elements are 

 understood in advance. It is then a comparatively simple 

 matter to study such elements in the three planes of section 

 and to trace their topography in the stem. It has seemed 

 desirable here to follow the second plan. 



PROSENCHYMA VERSUS PARENCHYMA 



The woody elements of Parashorea, as is the case in all woody 

 tissues, fall naturally into two groups — the prosenchymatous 

 and the parenchymatous — between which no hard and fast line 

 can be drawn. In general, prosenchyma consists of elongated, 

 thickened, dead cells with strongly lignified walls and pits which 

 are usually bordered. Prosenchymatous tissue performs two 



