12 



TREES OF THE NORTHERN UNITED STATES 



Fig. 1. 



Fig. 2. 



terial very durable and fit for furniture. A stem of this 

 kind is called endogenous (inside-growing). Fig. 1 repre- 

 sents a longitudinal and a cross section of an exogenous 



stem, and Fig. 2 of 



an endogenous one. 

 Since all the stems 



with which we have 



to deal are exogens, a 



particular description 



of that class will here 



be given. Fig. 1 shows 



the appearance of a 



section of an Ash 



stem six years old. 



The central portion, 

 which is about as thick as wrapping-twine, is the pith} 

 from this outward toward the bark can be seen the six 

 annual layers of the wood; and then comes the bark, con- 

 sisting of two portions. First there is an inside layer of 

 greenish material, the fresh-growing portion, and lastly 

 the outer or dead matter. This outer portion must crack 

 open, peel off, or in some way give a chance for the con- 

 stant growth of the trunk. The different kinds of trees 

 are readily known by the appearance of the bark of the 

 trunk, due to the many varieties of surface caused by the 

 allowance for growth. None of the characteristics of 

 trees afford a better opportunity for careful observation 

 and study than the outer bark. 



The Birches have bark that peels off in thin horizontal 

 layers the color, thinness, and toughness differing inthe 

 different species; the Ashes have bark which opens in 

 many irregular, netted cracks moderately near each other; 

 the bark of the Chestnut opens in large longitudinal 

 cracks quite distant from one another. The color of the 

 bark and the character of the scales are quite different 

 in the White and the Black Oaks. 

 In the woody portion radiating lines may be seen; 



