316 The Philippine Journal of Science iw* 



as the term implies, is associated with the vessels which it may 

 bound directly but from which it is usually separated by in- 

 tervening tracheids or fiber tracheids. The vasicentric pa- 

 renchyma may be restricted in amount to only a few cells, but 

 often exhibits a tendency toward extension tangentially, sug- 

 gesting eyelets, or even crosses one or more wood rays. This 

 is especially true of most species of Shorea and Hopea and of 

 Balanocarpus cagayanensis. 



The diffuse type may be represented by isolated cells that 

 border wood rays or are embedded in the midst of the libri- 

 form tissue, as in Anisoptera and Dipterocarpus, but the ar- 

 rangement is generally diffuse-zonate, in lines one (Hopea 

 plagata) or more (Isoptera borneensis, Hopea mindanensis) 

 cells in thickness which connect the wood rays and in which 

 the resin cysts are embedded. In fact, all gradations, from 

 the vasicentric through the vasicentric-zonate and diffuse-zonate 

 to the strictly diffuse type, are to be found. Vertical paren- 

 chyma is always present though seldom conspicuous in the wood 

 of the various species. 



The horizontal parenchyma of dipterocarp wood is confined 

 to the wood rays which vary appreciably in size and abundance, 

 not only in the wood of the different species of dipterocarps but 

 in different samples of the same species. Dipterocarpus, Ani- 

 soptera, and numerous species of Shorea, Pentacme, and Para- 

 shorea are characterized by large rays (sometimes one hundred 

 cells high by nine cells wide) which make up from 14 to 18 per 

 cent of the volume of the wood. The other extreme is repre- 

 sented by the finer-textured species of Hopea and Balanocarpus 

 where normally the rays do not exceed sixty cells in height and 

 five in width with which a reduced ray volume may or may not 

 be correlated. All gradations between these extremes occur, 

 but in general the finer-textured woods are characterized by 

 smaller rays. 



The individual rays are, without exception, of the heteroge- 

 neous type with distinct marginal cells which show to best ad- 

 vantage in radial section. Occasional rows of similar cells are 

 not infrequent in the body of the ray where two distinct types 

 of arrangement are to be noted. In the majority of cases they 

 are interpolated among the rows of normal cells throughout 

 the body of the ray, irrespective of the margin, and present 

 no unusual features. In Dipterocarpus and Anisoptera, to the 

 contrary, such interspersed rows are confined to the lateral 



