FOREST TREES AND FOREST REGIONS OF THE U. S. 6 



genera that make up 69 families, which in turn belong to 2 broad 

 classes of plants. Two of the families of trees, namely, those which 

 include the conifers (pines, spruces, firs, and others) and the yews, 

 belong to one of these classes known as gymnosperms, 4 and the other 

 67 families, consisting of the palms, yuccas, and hardwoods, belong 

 to the other class known as angiosperms. 5 



The northern white, shortleaf, longleaf, and western white pines 

 are examples of species of the genus Finns of the family Pinaceae 

 and of the class Gymnospermae. Popularly they belong to the coni- 

 fers or softwoods. The white, northern red, scarlet, and black oaks, 

 for example, are species of the genus Quercus of the family Fagaceae 

 and of the class Angiospermae. Popularly they belong to the broad- 

 leaf or hardwood group. 



In our forests are found 13 different groups or genera of true conifers, 

 2 of yews and tumions, 7 of palms, 1 of yucca, and 176 of hardwoods, 

 or a total of 199 genera. The conifers include 35 kinds or species of 

 pines, 7 spruces, 10 firs, 4 hemlocks, 3 larches, 12 junipers, and 19 

 others, mostly cedars and cypresses, or a total of 90 species. There 

 are 4 species of yews and tumions, and 21 species of palms and yuccas. 

 The hardwoods or broadleaf trees as a group are composed of 61 

 native species of oaks, 18 hickories, 19 ashes, 14 cherries, 11 plums, 

 10 apples, 17 maples and boxelders, 7 birches, 6 elms, 15 cottonwoods 

 or poplars, 22 willows, 178 hawthorns, 5 gums, 6 hackberries, 9 

 magnolias, and 297 species of other genera to which, for example, 

 belong beech, persimmon, dogwood, mulberries, locusts, holly, and 

 walnuts, and many others, making a total of 695 species of hardwoods. 

 Altogether, the above makes a grand total of 810 species of native 

 trees in the United States. 



Many kinds of trees attain heights of 100 feet, and a few heights 

 of 300 to 350 feet. Many are small in size. Under varying conditions 

 of climate and soil, some occur both as trees and shrubs. If a woody- 

 stemmed plant has one well-defined trunk and grows to be at least 2 

 inches in diameter and 8 feet in height, it is classed as a tree species. 



The natural home or range of trees varies greatly. Some are found 

 widely over a vast area, such as beech, American elm, black willow, 

 white and black oaks, shortleaf pine, and eastern red cedar. A few, 

 including white spruce, dwarf juniper, aspen, balsam poplar, paper 

 birch, peachleaf and (Bebbs) willows, coralbean and buttonbush, 

 range practically across the continent in the United States, while a 

 few others, like the black spruce and tamarack, extend across the con- 

 tinent, partly in the United States and partly in Canada. The wild 

 plum, honey mesquite, hoptree, boxelder, leucaena, and nannyberry 

 occur in both the eastern and western divisions of forest regions. The 

 Torrey pine is confined to an area of about 40 acres in the extreme 

 southern part of California. Southward, the number of native tree 

 species increases. From a maximum of 60 to 80 species occurring 

 in any one northern State along the Canadian border, the number 

 increases to some 200 in the Middle Atlantic region (for example in 

 North Carolina), and in Florida reaches a maximum of about 350, of 

 which more than 100 are tropical and occur exclusively in that State. 



4 Gymnosperms are plants whose seeds are borne openly on a naked scale or bract. 



8 Angiosperms are plants with seeds enclosed in an ovary and bearing the more common kinds of flowers. 

 There are two divisions. The yuccas and palms as a group are known as monocotyledons (having one 

 cotyledon in the seed embryo, parallel-veined leaves, and other characteristics), and the broadleaf or hard- 

 wood trees as dicotyledons (with two cotyledons in the seed embryo, netted veins, and annual rings of 

 growth in the stem or trunk). 



