382 



STRUCTURE OF PHANEROGAMIC PLANTS. 



present) intervene between any pair of them. In the longitu- 

 dinal section taken in a radial direction (Fig. 171), and conse- 



Fro. 171. 



FIG. 172. 



Fig. 171. Portion of vertical section of the same wood, taken in a radial direction, showing the 

 glandular woody fibres, without ducts, crossed by the Medullary Rays, a, a. 



Fig. 172. Portion of vertical section of the same wood, taken in a tangential direction, so as to 

 cut across the Medullary Rays. 



quently passing in the same course with the medullary rays, 

 these are seen as thin plates (a, a, a) made up of superposed cells 

 very much elongated, and crossing, in a hori- 

 FIG. 173. zorital direction, the glandular woody fibres 



which lie parallel to one another vertically. 

 And in the tangential section (Fig. 172), 

 which passes in a direction at right angles 

 to that of the medullary rays, and therefore 

 cuts them across, we see that each of the 

 plates thus formed has a very limited depth 

 from above downwards, and is composed of 

 no more than one thickness of horizontal 

 cells. A section of the stem of Mahogany, 

 taken in the same direction as the last (Fig. 

 173), gives a very good view of the cut ends 

 of the medullary rays, as they pass between 

 the woody fibres ; and they are seen to be 

 here of somewhat greater thickness, being 

 composed of two or three rows of cells, ar- 

 ranged side by side. In another fossil wood, 

 whose transverse section is shown in Fig. 

 174, and its tangential section in Fig. 175, 

 vertical section of Mahogany. the me( j u iiaiy rays are seen to occupy a 



much larger part of the substance of the stem ; being seen in the 

 transverse section as broad bands (a a, a a), intervening between 

 the closely set woody fibres, among which the large ducts are 

 scattered ; whilst in the tangential, they are observed to be not 



