14 TREES 



"filling" with varnish or other substance before they can 

 be satisfactorily poKshed. Fine-grained woods, if hard, 

 polish best. Trees of slow growth usually have fine- 

 grained wood, though the rule is not universal. 



Ordinarily wood fibres are parallel with their pith. They 

 are straight grained. Exceptions to this rule are con- 

 stantly encountered. The cliief cause of variation is the 

 fact that tree trunks branch. Limbs have their origin in 

 the pith of the stems that bear them. Any stem is nor- 

 mally one year older than the branch it bears. So the 

 base of any branch is a cone quite buried in the parent 

 stem. A cross-section of this cone in a board sawed from 

 the trunk is a knot. Its size and number of rings indicate 

 its age. If the knot is diseased and loose, it will fall out, 

 leaving a knot hole. The fibres of the wood of a branch are 

 extensions of those just below it on the main stem. They 

 spread out so as to meet around the twig and continue in 

 parallel lines to its extremity. The fibres contiguous to 

 those which were diverted from the main stem to clothe 

 the branch must spread so as to meet above the branch, else 

 the parent stem would be bare in this quarter. The union 

 of stem and branch is weak above, as is shown by the clean 

 break made above a twig when it is torn off, and the stub- 

 born tearing of the fibres below down into the older stem. 

 A half hour spent at the woodpile or among the trees with a 

 jack-knife will demonstrate the laws by which the straight 

 grain of wood is diverted by the insertion of limbs. The 

 careful picking up and tearing back of the fibres of bark 

 and wood will answer all our questions. Bass wood whose 

 fibres are tough is excellent for illustration. 



When a twig breaks off, the bark heals the wound and 

 the grain becomes straight over the place. Trees crowded 



