302 The Philippine Journal of Science 1923 



composed of elongated cells with oblique end walls and dark 

 brown contents and conspicuous because of their darker color. 

 The larger rays, which are multiseriate and consist of four to 

 six rows of cells, pursue a straight course across the field 

 except for slight deflections where they are contiguous to or 

 approach the larger pores. At such points they curve slightly, 

 while the pores are somewhat flattened on the side of contact. 

 Where vessels abut on opposite sides of the ray, the latter 

 becomes very much restricted where it extends between them. 



Interspersed between the larger bands are smaller rays which, 

 at the start at least, consist of but a single row of cells com- 

 parable in every way to those which compose the multiseriate 

 type. The course of the uniseriate rays across the field is much 

 more irregular than that of the multiseriate rays, since they 

 curve around the pores that lie in their course and are not of 

 sufficient size to cause them to become flattened. As will be 

 pointed out subsequently, the narrow rays of the cross section 

 are in part uniseriate throughout their vertical length, and in 

 part the margins of multiseriate rays which happen to be in- 

 cluded in the plane of section. It is from the uniseriate rays that 

 the tyloses of the vessels are mainly derived. The light areas 

 of small cells about the pores are a feature of many tropical 

 woods and they consist, in Parashorea, of tracheids and vertical 

 parenchyma (Plate 22). The tracheids, like the vessels, are 

 organs of conduction and mechanical support, and are strictly 

 vasicentric. They are found only in regions contiguous to 

 vessel walls and occur in the angles between coterminous vessels, 

 or vessels and wood rays (Plate 3). 21 The paratracheal or 

 vasicentric parenchyma, on the contrary, separates the libriform 

 tissue from the vessels and tracheids and may adjoin the ducts 

 directly or abut upon the tracheids neighboring them. It per- 

 forms mainly the storage function and is in intimate connection, 

 on the one hand, with the ray cells from which it obtains food 

 for storage and, on the other, with the vessels direct or through 

 the intervening tracheids into which it pours food in solution at 

 periods of growth optima. Tracheids and vertical parenchyma 

 together constitute from 14 to 19 per cent of the wood. 



The libriform fibers (wood fibers), which are the principal 

 mechanical elements, make up the background for the other 

 cells, and form from 35 to 40 per cent of the volume of the 



