PLVUS SYLVESTRIS. 149 



section of one or more of the horizontal branches con- 

 necting neighboring ducts. The structure is most 

 easily made out in those of the xylem, those of the 

 phloem being too large to allow a complete section to 

 be easily obtained.) Note 



a. The empty cells forming the sheath ; their shape. 



b. The secreting parenchyma cells lining the duct ; 

 shape and contents. 



25. The bases of the scale leaves. Note 



a. The delicate thin-walled cells forming their inner 

 portion. 



b. The rather thick-walled cells, sclerenchyma, form- 

 ing the outer part. 



c. The very thick-walled outer row, the epidermis, 

 with thickly pitted walls. 



d. The very thick cuticle. 



e. The contents ; note color. 



26. Draw a portion of the section, showing all the above 

 points. 



Cut a longitudinal tangential section, passing through 

 the wood. Examine with a high power, and note 



27. The cut ends of the medullary rays, wedged between 

 the fibers of the xylem. Notice 



(7. The number of rows of cells in the thickness and 

 height of each ray. 



b. The thin parts of the walls corresponding to the 

 pits (see A. 18. b. v.). 



c. Make a drawing of one of the rays, showing also 

 a few adjacent tracheides. 



28. The numerous sections, in different directions, through 

 bordered pits. Study these sections further, if necessary 

 to an understanding of the structure of the pits. 



