THE FORMATION OF WOOD. 



21 



these ducts are scat- 

 tered througli the 

 whole season's growth, 

 and in all conifers, as 

 for example the Pines 

 and Cedars, they are 

 entirely wanting. 

 But the differences in 

 hardness and color 

 between the growth 

 of spring and summer 

 are still present. It 

 is sometimes possible 

 to see the line which 

 separates the growth 

 of two seasons in the 

 bark, as in the case of 

 common cork, which 

 is the outer bark of 

 the Cork Oak, a na- 

 tive of southern Eu- 

 rope. (See ^g. 15.) 



If the trunk or 

 branch of an Oak 

 tree is cut smoothly 

 across, thin whitish 

 lines may be seen run- 

 ning from within out- 

 ward. Some of these 

 lines begin in the cen- 

 ter of the tree, and 

 others in each one of 

 the annual rings. 



Fig. 21. — A section of the comiuon Staghom 

 Sumach, showing the darkened lieartwood, 

 the white sapwood, and the inner and outer 

 bark. Dark coloring matter is often de- 

 posited in the heartvrood, as in the case here 

 shown. Milford, Pa. 



