SYLVESTRIS. 143 



Examine with a high power and study 



8. T\i& pith parenchyma. Note 



a. The shape and arrangement of the cells ; the modified 



shape of those passing out to a dwarf branch. 



b. The contents. Test with iodine. 



9. The xylem. Notice that the salient angles of the pith 

 divide it more or less completely into wedge-shaped 

 bundles. Studying one of these wedges, note 



a. At the apex one or two resin ducts. Study their 

 structure, noticing 



The shape of the opening. 

 The circle of rather delicate cells lining the 

 duct, the secreting layer. Note the granular 

 nucleus in each, nearly filling the cell. 

 iii. The quite irregular circle of flattened cells, 

 with longer diameters parallel with the circum- 

 ference, bounding the duct, the sheath. 



b. Between the resin duct and the pith, forming the 

 point of the wedge, a group of several spiral and 

 reticulated vessels. These are rather difficult to 

 distinguish from the wood cells. They may be 

 recognized by their slightly thicker walls, the 

 smaller diameter and rounder shape of their 

 cavities. On staining the section slightly with 

 magenta, they take a somewhat deeper color than 

 the wood cells. After the section has lain for some 

 time in glycerine they may be recognized by their 

 greater opacity. 



c. Forming the bulk of the xylem, the wood cells or 

 fibers. On account of the similarity of the mark- 

 ings (to be studied later) on their walls to those on 

 tracheae or vessels, they are called tracheides. 

 Note 



