114 BOTANY: PRINCIPLES AND PROBLEMS 



353. Wood has a "grain" which in general runs parallel to the axis 

 of the tree. To what is this grain due? 



354. Whj^ does wood split easily "with the grain" but not "against 

 the grain?" 



355. What causes knots in wood? 



356. A log otherwise free from knots often shows them near its center. 

 Why? 



357. Which will have more and larger knots in its wood, a tree grown 

 in the forest or one grown in the open? Why? 



358. Why is the wood of knots apt to be harder than the wood around 

 them? 



359. Which will decay faster if exposed freely to the air, heart-wood or 

 sap-wood. Why? 



360. By looking at the cut end of a board, how can you tell the 

 position which this board held with reference to the center of the log 

 from which the board was cut? 



361. How can you tell whether a piece of furniture is made of veneered 

 wood or not? 



362. What two ways do you know for telling the age of a twig? 



363. What makes the annual rings in wood clearly distinct from one 

 another? 



364. What often makes it difficult to count the annual rings of trees 

 which have grown in warm regions? 



365. As a tree grows older, which increases more rapidly in thickness, 

 its heart- wood or its sap-wood? Explain. 



, 366. In most woody plants it is only the last year's growth of bast, or 

 at most that of the last few years, which functions in translocating food. 

 Explain. 



367. Of what use are the bast-fibers to the plant? 



368. What suggestion can j^ou make as to the function of the com- 

 panion-cells in the bast? 



369. How would you prove that the ascending stream of water travels 

 in the wood? 



370. Species of trees differ markedly in the height to which they can 

 grow. Can you suggest a factor which may be responsible for this 

 difference? 



