The Structures and Processes of Stems 137 



6. \\'hy is lumber seasoned by piling it in lumber yards for months or years 

 before it is used? 



7. What is charcoal? How is it manufactured? What are its uses? 



8. Why is charcoal made from peach and apricot pits and the shells of nuts pre- 

 ferred as an absorbent in gas masks? 



9. What commercial products are made by the distillation of wood ? 



10. What substances are used to preserve railroad ties and posts from decay? 

 From what are these substances derived? 



