124 PRACTICAL COURSE IN BOTANY 



the wood. The longer a dead branch remains on a tree the 

 more rings of growth will form around it before covering it up, 

 and the greater will be the disturbance caused by it. Hence, 

 timber trees should be pruned while very young, and the 

 parts removed should be cut as close as possible to the main 

 branch or trunk. Sometimes knots injure lumber very much 

 by falling out and leaving the holes that are often seen in pine 

 boards. In other cases, however, when the knots are very 

 small, the irregular markings caused by them add greatly 

 to the beauty of the wood. The peculiar marking of bird's- 

 eye maple is caused by abortive buds buried in the wood. 



Practical Questions 



1. Is the swelling of wood a physical or a physiological process? 



2. Does wood swell equally with the grain and across it ? (Suggestion: 

 test by keeping a block under water for 10 to 20 days, measuring its dimen- 

 sions before and after immersion.) 



3. In building a fence, what is the use of "capping" the posts ? (133.) 



4. In laying shingles, why are they made to touch, if the work is done 

 in wet weather, and placed somewhat apart, if in dry weather? (136.) 



5. What is the difference between timber and lumber? Between a 

 plank and a board ? Between a log, stick, block, and billet ? 



6. Why does sap wood decay more quickly than heartwood? (131.) 



7. Explain the difference between osmosis, diffusion, capillarity, and 

 imbibition. (9, 56, 57, 136; Exp. 53.) 



VI. FORESTRY 



138. Practical bearings. -- This part of our subject is 

 closely related to lumbering and forestry. The business of 

 the lumberman is to manufacture growing trees into mer- 

 chantable timber, and to do this successfully he must under- 

 stand enough about the structure of wood to cut his boards 

 to the best advantage, both for economy and for bringing out 

 the grain so as to produce the most desirable effects for 

 ornamental purposes. 



139. Forestry has for its object: (1) the preservation 

 and cultivation of existing forests ; (2) the planting of new 



