186 TREES IN- WINTER 



The color of the outer bark is an important mark of distinction 

 and is the chief means of separating the different species of the 

 Birches (p. 281-291). The color and taste of the inner layers 

 of the bark are in some cases also characteristic. The Black 

 Oak for example is best distinguished from other Oaks by the 

 yellow and intensely bitter inner bark. Similarly, the Black Birch, 

 the Sassafras and the genus Prunus including the Cherries have 

 b'arks with characteristic flavors. The swamp-loving Poison 

 Sumach (p. 395) is the only poisonous tree in New England so 

 that after this shrubby form is known there need be no fear of 

 tasting bark and twigs of any unknown tree-like species. 



The bark varies in character according to the age of the tree. 

 In the young tree the bark is smooth, but, as the trunk expands 

 from the growth of the wood within, the covering of dead bark 

 outside is forced to crack in a variety of ways giving rise to 

 characteristic fissures and ridges which become more prominent 

 as the tree grows older. The bark of few trees such as the Beech 

 (p. 295) and the American Hornbeam (p. 279) remain smooth, 

 their outer layers expanding with the growth of the tree. The barks 

 of others as the Paper and Yellow Birch (p. 283) stretch and peel 

 off in thin papery layers. In the Birches (p. 289) and Cherries 

 (p. 369) the breathing pores (lenticels) become horizontally elon- 

 gated to form narrow transverse streaks which are characteristic for 

 these forms. When ridges or scales are formed they may be close 

 and firm and with difficulty removed from the trunk as is the case 

 with the bark in the Black Oak group or, on the other hand, they 

 may be easily rubbed off as are the scales of the bark of the 

 White Oak and of most members of the White Oak group. Bark 

 of this latter type is called flaky in our descriptions and this 

 distinction between barks that are flaky and those that are not 

 flaky is of considerable importance in classification. To avoid 

 confusion little notice is taken of the minute scales that are 

 likely to occur on the surface of both types of bark. The bark 

 may come off in large sheets as in the Shag-bark Hickory (p. 269) 

 and the Sycamore (p. 349), and the ridges may be long as in 

 the Chestnut (p. 297) or short and run together to fonn more 

 or less perfect diamond-shaped areas as in the White Ash (p. 423) 



