PIN US S YL VES TRIS. 1 45 



walls of some of these cells will be found perfor- 

 ated by clusters of very fine pits, looking like 

 fine parallel lines passing across the wall. These 

 are sections of \htsieveplates; they occupy the 

 same relative position as the sections of the bor- 

 dered pits of the tracheides. Note the shape of 

 the sieve cells next the cambium and next the 

 cortical parenchyma. 



/>. Near the periphery of the sieve tissue an inter- 

 rupted row of cells with brown or yellow contents 

 in which are strongly refringent crystals. Near 

 the cambium a similar row of cells, larger and 

 rounder than the sieve cells and with colorless or 

 slightly yellowish homogeneous contents, in which 

 a small crystal or two may sometimes be seen. 

 These two broken rows of cells are \hz phloem- 

 parenchyma? 



12. The cortical parenchyma. Note 



a. The shape, size and arrangement of the cells. Com- 

 pare with pith parenchyma. 



b. The contents. 



c. The very large resin ducts. Compare their struct- 

 ure with those of the xylem (A. 9. a.). Note the 

 cells of the sheath, larger, thicker-walled and not 

 flattened as are those surrounding the ducts in the 

 xylem ; the secreting cells, similar to but more 

 numerous than those of the xylem ducts. 



13. The medullary rays. In a thin part of the section 

 note 



a. Their extent, from pith to cortical parenchyma. 



9 Can be brought out by staining with chlor-iodide of zinc and better 

 still by methyl blue. 



