36 



come furrowed later, while many other species become rough early 

 in life. The manner in which the bark cracks open or peels off af- 

 fords a ready means of identification for many of our trees. The 

 exfoliation of the bark is rather constant for each species. In some 

 species like the Yellow Birch and Paper Birch it peels off in thin 

 film-like papery layers. In the Shag-bark Hickory it is shaggy; in 

 many species like the Pines and Spruces it is scaly; while in others 

 like the White Cedar it is shreddy. Many species have furrowed 

 bark. The furrows run usually in a longitudinal direction but may 

 run transversely. The furrows or fissures separate ridges. These 

 vary with the species. The fissures may be short or long, close or 

 distant, narrow or wide, longitudinal, transverse, or diagonal. The 

 ridges may be pointed or broad, high or low, smooth or scaly. The 

 bark may be broken up into small square or rectangular blocks as 

 in the Black Gum. This form of bark is often spoken of as "alli- 

 gator bark." See Figures 44-103 for bark of most of our important 

 native trees. 



The bark may be of considerable technical value. Hemlock and 

 some species of Oak and Spruce have bark which is rich in tannin. 

 The bark of these species is used extensively in the leather industry. 

 The bark of a European species of Oak is highly prized on account 

 of the large quantity of cork which it produces. The inner bark of 

 some species yields dyeing material while that of others is used in 

 the manufacture of fibre cloth. Formerly the bark of the Paper 

 Birch was used in the construction of canoes. 



3. Twigs : 



Twigs are the terminal parts of branches. The term twig usually 

 refers to that portion of the terminal part of the branch which 

 grew in the last season. Those portions of the branch which began 

 their growth a few seasons ago are usually spoken of as older twigs 

 or branchlets. The twigs have their origin in the vegetative buds 

 which may be located on the terminal end of the twig of the previous 

 season's growth or along its side. If they emerge from terminal 

 buds they become leaders, and if from lateral buds they will develop 

 into lateral branches. The lateral branches may be alternate^ op- 

 posite, or wJiorled (Plate II). The method of branching is very help- 

 ful in distinguishing our common trees. The lateral branches of most 

 of them alternate with each other, while a fair number are opposite 

 and a few whorled. The terminal twig elongates rapidly while the 

 lateral ones usually remain shorter and occasionally are compressed 

 to a stub or spur. 



When the vegetative buds burst open in spring young twigs, 

 which are often covered with developing leaves, emerge from them. 

 These twigs are, at first, usually delicate, greenish in color, and 



