306 The Philippine Journal of Science 1923 



the periphery of the tree increases, it follows that ray flecks may 

 begin or run out at any point in the wood, depending on the 

 orientation of the section. 



Occasionally, a row of resin cysts may be seen running longi- 

 tudinally in the wood and appearing as a series of cavities 

 surrounded and connected by parenchyma. The first impression 

 is that a resin duct has run out of the plane of section only 

 to reappear at another point, but this idea can be dissipated 

 by reference to cross sections where it is not uncommon to find 

 masses of parenchyma in place of the so-called resin ducts. The 

 resin cavities of Parashorea consist of a series of vertical 

 cysts separated by masses of parenchyma and are comparable to 

 the traumatic cysts of the Coniferae. 



The epithelial parenchyma bordering the resin cysts, as seen 

 in radial section, consists of cells that are either isodiametric or 

 but slightly elongated longitudinally and, as noted in the cross 

 section, arch into the cavity. These are followed laterally and 

 at the top and bottom by other cells that are elongated in the 

 direction of the grain and grade into typical parenchyma. The 

 tracheids which border vessel cavities are not found near the 

 centers of resin formation. 



As in the cross section the remainder of the area is occupied 

 by extensive tracts of libriform fibers, which are so closely 

 crowded that the contour of the individual elements cannot be 

 followed with any accuracy. The tissue presents a striated 

 appearance, which owes its origin to the thick walls of the 

 libriform cells set off by the narrow lumina alternating with 

 them, and is easily distinguishable from the portions of the wood 

 reserved for conduction and storage. It follows that the con- 

 tour and extent of the patches of mechanical tissue must of neces- 

 sity vary widely, not only in different sections but in different 

 parts of the same section, since their orientation with regard to 

 the other elements is purely accidental in a diffuse porous wood 

 of this type. Laterally they are margined by parenchyma bor- 

 dering resin cysts and vessels, and vertically by ray flecks. In 

 addition the regularity is broken here and there by rows of 

 vertical parenchyma, which formation is often changed through 

 subsequent septation into catenate strings of idioblasts. The 

 latter are prominent owing to the size of the crystals. 



Tangential section.— (Plate 8.) The tangential section de- 

 parts strikingly in appearance from the radial owing to the fact 

 that the wood rays are now seen transversely as fusiform struc- 

 tures with their long axes directed longitudinally. They are typ- 



