WOOD STRUCTURE 



169 



Compare the graining of your specimens, or of the floor- 

 ing, window casings, doors, desks, benches, etc., of your 

 schoolroom with Figures 312 and 313, and tell what kind 



315- 



-Sections of sycamore wood (from PiNCHOT, U.S. Dept. of Agr.) : 

 u, tangential ; d, radial ; f, cross. 



of cut was made in each case and show how the appearance 

 of the timber has been affected by it. 



239. Knots. — Look for a billet with a knot in it. Notice 

 how the rings of growth are disturbed and displaced in its 

 neighborhood. If the knot is a large one, it will itself 



316. — Sections of white pine wood (from PrNCHOT, U.S. Dept. of Agr.). 



have rings of growth. Count them, and tell what its age 

 was when it ceased to grow. Notice where it originates. 

 Count the rings from its point of origin to the center of 

 the stem. How old was the tree when the knot began to 

 form .' Count the rings from the origin of the knot to the 



