PRACTICAL WORK 343 



wood and the rays as " silver grain," because their course is 

 sinuous. On the tangential face the rays are seen in their lens- 

 shaped transverse section, and their vertical extent can be 

 determined. 



Note on the transverse and radial faces the distinction between 

 heartwood and sap wood. 



(6) Draw under the high power a small portion of a cross- 

 section of the outer tissue of the stem of a woody plant during 

 its first summer's growth to show the origin of the phellogen 

 and the development of cork [Ailanthus is suitable]. Compare 

 the remaining tissues of the stem with (3). 



(7) Examine the piece of willow branch provided. Observe 

 the lenticels on the surface. Peel the branch and note that the 

 bark separates along the line of the cambium. 



