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PLANTS AND MAN 



the entire eastern half of the United States. Most are small trees 

 about forty feet in height and little over a foot in diameter, but 

 the southern forms reach heights of over one hundred feet with 

 diameters up to four feet. It is extremely rapid growing, reaching 

 maturity in about sixty years, and having a light, soft and weak 

 wood. Because of its rapid growth and its dense root system, this 

 and other tree willows are widely used for planting along stream 

 banks and levees where it is essential that the soil be firmly 

 anchored against the erosive forces of running water. 



The Aspens, Cottonwoods, and Balsam Poplars 



This genus (Populus) includes fifteen tree species, less than 

 half of which are of commercial importance. The leaves are 

 alternate, oval to triangular, sometimes toothed or lobed, and 

 generally have long stalks which are often flattened in cross 



section (fig. 200). The twigs 

 possess terminal buds and 

 lateral buds of about the same 

 size, all covered with over- 

 lapping scales, which in some 

 species are very resinous. 

 Poplar flowers are very similar 

 to those of the willows. 



The TREMBLING ASPEN haS 



the distinction of being the 

 most widely distributed tree in 

 North America, ranging trans- 

 continentally from Labrador 

 to northern Alaska, and south- 

 ward to southern California, 

 the southern Rocky Mountains, and the Ohio valley. The 

 leaves are broadly circular in outline, pointed, with minute, 

 rounded teeth, and a laterally flattened stalk which causes 

 them to "tremble" in the slightest breeze. It is usually a 

 small tree not over sixty feet in height, extremely fast growing 

 and short lived with a light, soft, weak, close-grained wood. 

 Similar in all commercial respects to the trembling aspen is the 

 LARGETOOTH ASPEN, which differs botanically in having its 



Fig. 200. — Poplars have, long- 

 stalked leaves, alternately arranged 

 on the stem. 



