22,s Reyes: Woods of the Philippine Dipterocarps . 307 



ically diffuse in arrangement and vary in height from ten to sixty 

 cells and in width from one to six cells, respectively. The cells on 

 the upper and lower edges are larger (heterogeneous) and appear 

 cuneiform, conforming with the contour of the ray, while those 

 in the body vary from orbicular to ovoid or polygonal and meas- 

 ure from 10 to 54 ^. 24 All the cells contain organic matter, 

 which either fills the lumina or occurs as a thin layer lining the 

 wall. The horizontal resin ducts, described by Pfeiffer in the 

 wood rays of three of the Javanese dipterocarps,-' are totally 

 wanting in Parashorea. 2 * 



Aside from the vessels, the vertical elements present the same 

 features as in the radial section and require no further dis- 

 cussion here. They follow a sinuate path, owing to deflections 

 occasioned by the larger rays, in contrast to their straight course 

 in the radial section. In addition the individual vessel segments 

 differ in appearance in that the terminal constriction which is 

 perforated is now seen to be slightly oblique ; where a segment 

 is seen in median section, the points of constriction are no 

 longer opposite each other, indicating that the vessel segments 

 arise from fusiform initials similar to those which give rise to 

 tracheids but have reached a high stage of development. 27 



The tangential section likewise affords the best opportunity 

 to observe the formation of tyloses. As noted previously these 

 arise from parenchyma which is contiguous to vessels and in 

 Parashorea is traceable to wood rays, more especially the uni- 

 seriate rays. The latter are abruptly deflected where vessels 

 intercept their course, curve around them, and subsequently 

 form tyloses along the line of contact, which in tangential sec- 

 tions appear as lateral cystlike structures emanating from the 

 rays. Whether or not tylosic formation, which owes its origin 

 to the proximity of a vessel, results in this case from tension 

 in the ray cells is debatable, but it seems reasonable to assume 

 that this condition exists. 



" The cells along the lateral margins tend to be somewhat larger than 

 those deeper within the body of the ray. 



* Pfeiffer, J. Ph., De Waarde van Wetenschappelijk Onderzoek voor de 

 Vaststelling van Technische Eigenschappen van Hout. Amsterdan, J. H. 

 de Bussy (1917). 



" I have observed horizontal resin ducts in only one of the thirty-two 

 species of Philippine dipterocarps that I have examined. This is Shorea 

 mindanensis Foxworthy, a species restricted to Mindanao and Basilan. 



" See Jeffitey, E. C, The Anatomy of Woody Plants. University of 

 Chicago Press (1918). 



