22. s Reyes: Woods of the Philippine Dipterocarps 317 



margins of rays and appear in tangential section as large cells 

 bounding a central core of smaller elements. The significance of 

 the latter arrangement has not as yet been determined. 



As is often the case in other tropical families, dipterocarp 

 woods are characterized by the presence of more or less extra- 

 neous organic matter which takes the form of amorphous brown 

 infiltrations in the lumina of the parenchyma cells. Such or- 

 ganic products are usually confined to the ray cells and, as seen 

 microscopically, appear as gummy incrustations lining the walls 

 or filling the lumina entirely and then rendering the details of 

 pit structure obscure. Rarely is the vertical parenchyma in- 

 volved, and only when the ray cells are thoroughly impregnated 

 is there an apparent leakage into the vertical cells. Such or- 

 ganic infiltrations may be reserve food which was not utilized 

 in the further growth of the tree or, on the other hand, may be 

 by-products of metabolism which have been deposited in the ray 

 cells. These infiltrations are very distinct in the red lauaans 

 such as Shorea negrosensis and Shorea polyspermia; in fact, these 

 woods in part owe their color to them. The paler white lauaans, 

 on the contrary (Shorea mindanensis, Pentacme contorta, and 

 Anisoptera spp.), are characterized by meager organic infiltra- 

 tion. 



Idioblasts are present in the majority of dipterocarp woods 

 and, as previously pointed out, have their origin in parenchyma, 

 in both the vertical and the horizontal wood rays. Such cells 

 usually become further segmented by secondary septa into a 

 number of compartments in each of which a tetragonal crystal 

 of calcium oxalate is formed. Where the rows of vertical 

 parenchyma are involved, catenate strings result which stand 

 out in section against the remaining tissue ; on the other hand, 

 it is not uncommon to find all the cells of a wood ray modified 

 into idioblasts. 



Idioblasts are of some diagnostic value owing to their varying 

 distribution in the different species, a feature that has been em- 

 ployed to advantage in the following keys. For example, both 

 kinds are present in Parashorea malaanonan, Hopea acuminata, 

 H. mindanensis, and in species of Pentacme. In contrast to 

 the above, vertical idioblasts are wanting in Vatica mangachapoi, 

 Hopea plagata, and a few other forms, which is also true of the 

 horizontal idioblasts in Isoptera borneensis, Shorea balangeran, 

 and S. guiso. Further study and examination of many samples 

 of each species are necessary, however, to verify the value of 



