THE STRUCTURE OF WOOD. 



37 



The term "grain" may also mean the "figure" formed by the 

 presence of pith rays, as in oak, Fig. 32, or beech, or the word "grain" 

 may refer simply to the uneven deposit of coloring matter as is com- 

 mon in sweet gum, Fig. 33, black ash, or Circassian walnut. 



The presence of a limb constitutes a knot and makes great irregu- 

 larity in the grain of wood, Fig. 34. In the first place, the fibers on 

 the upper and lower 

 sides of the limb behave 

 differently, those on the 

 lower side running un- 

 interruptedly from the 

 stem into the limb, while 

 on the upper side the 

 fibers bend aside making 

 an imperfect connection. 

 Consequently to split a 

 knot it is always neces- 

 sary to start the split 

 from the lower side. On 

 the other hand it is eas- 

 ier to split around a 

 knot than thru it. The 

 texture as well as the 

 grain of wood is modi- 

 fied by the presence of a 

 branch. The wood in 

 and around a knot is 

 much harder than the 

 main body of the trunk 

 on account of the crowd- 

 ing together of the ele- 

 ments. Knots are the 



remnants of branches left in the trunk. These once had all tht parts 

 of the trunk itself, namely bark, cambium, wood, and pith. Nor- 

 mally, branches grow from the pith, tho some trees, as Jack pine and 

 redwood, among the conifers, and most of the broad-leaf trees have 

 the power of putting out at any time adventitious buds which may 

 develop into branches. When a branch dies, the annual layer of 

 wood no longer grows upon it, but the successive layers of wood on 



Fig. 31. Bnrl on White Oak. 



