PINUS AUSTRIACA, OR P. LARICIO. 135 



c. The resin-ducts. Compare their structure with that 

 of the ducts in the xylem. 



7. By use of a very thin section study the medullary rays, 



observing : 



a. The rays extending from the pith to the cortical paren- 

 chyma. 



6. The shape of the cells in the xylem and the gradual 

 transition into the cortical parenchyma. 



c. The cell contents. 



8. The outermost part of the stem is composed of the bases 



of the scale-leaves. In one leaf-base observe: 



a. An inner layer of very thin-walled irregular cells. 



b. An outer layer of one or two rows of large cells upon 

 which is a single row of epidermal cells. Observe: 



i. The thickening of the outer epidermal wall, and 

 ii. The continuous outer layer of this wall, the cu- 

 ticle. 



9. Make a diagram of the entire cross section and label the 

 various regions. 



10. Draw in detail a narrow strip including all kinds of stem 

 tissues from pith to epidermis. 



11. Make a thin longitudinal radial section of a year-old stem, 

 and identify by their arrangement the various kinds of 

 tissues seen in the transverse section, and study the differ- 

 ence in shape of cells in this section. 



12. Draw in detail small regions which show structures not 

 seen in cross-section. 



Make a thin tangential section through the wood. Observe 

 especially: 



13. Ends of medullary rays. 



a. The number of rows of cells in thickness and height of 

 each ray. 



b. The thin parts of the walls corresponding to the pits. 



c. Draw, including a few adjacent tracheids. 



