138 LABORATORY AND FIELD EXERCISES 



(2) Storage tissues of the xylem. Is the spruce as well 



provided with storage tissues as the above- 

 mentioned stems ? How does it compare with 

 the storage system of the fern stem ? Is the 

 spruce intermediate in this respect between 

 the alder and the fern ? Be able to explain. 



(3) Drawings. Outline a sector of a transverse section 



of the spruce stem. Detail in this sector the cork 

 layer, a small portion of the xylem at the junction 

 of two annual rings, a leaf gap, and a leaf trace. 



LONG SECTIONS 



Study thin sections cut from spruce or pine to determine the 

 structure of the water-carrying tracheids and of the wood rays. 

 Mount in alcohol if freshly prepared material is used. 



1. Tracheids. What is the nature of the conducting elements, 



or tracheids, making up the wood of pine or spruce ? 

 Are they single cells ? What is their shape ? What are 

 their surface markings ? How do they differ from the 

 vessels, or trachea?, of the higher plants studied earlier 

 in the course ? Compare the ducts of the lilac and alder 

 with the tracheids in your slide. Do the wall mark- 

 ings of tracheids differ from those of ducts ? Study the 

 bordered pits on the walls of the tracheids, consulting 

 the text concerning their structure. On which walls 

 of the tracheids are the bordered pits, the tangential 

 walls or the radial walls ? 



2. Wood rays. If rays are seen in radial sections, note the 



differentiation of their cells into living starch-bearing 

 cells and dead water-conducting tracheids. 



3. Drawings. Draw a small portion of your section accurately 



to show the structure of tracheids and wood rays. 



