258 PLANTS AND MAN 



considerably softer than that of a "softwood" (ponderosa or 

 longleaf pine). Similarly, many of the "evergreens" shed theif 

 leaves during the winter (larches, bald cypress), and are in 

 actuality, deciduous rather than evergreen. Both the evergreen 

 and deciduous leaf habits have their advantages and disadvan- 

 tages. The evergreen habit permits the tree to manufacture food 

 during temporary warm periods in the winter season, while the 

 deciduous tree, being leafless cannot do this. On the other hand, 

 the evergreen leaves, though protected by wax coverings against 

 excessive drying, may lose water faster in the drying winter winds 

 than the roots can absorb it from the frozen soil. This is one factor 

 contributing to the appearance of a timberline at high altitudes 

 and in the far north. 



The total number of coniferous species native to the United 

 States is about one hundred, distributed through fifteen genera, 

 the most common of which are the pines, spruces, hemlocks, 

 arbor vitaes, and cedars. 



The Pines 



The pines (Pinus) (fig. 181) have thick, needle-like leaves 

 which are borne in clusters of two to five, at the tips of very short 

 branchlets which are inconspicuous and drop off* when the leaves 

 are shed, after periods of five to seven years on the treq. The cones 

 vary greatly in size and shape but are always pendent and have 

 thick, woody scales upon which the seeds are borne. 



This constitutes the largest and most important genus of all 

 the conifers. Excluding Mexico, North America has about thirty 

 five native species of pines, and one or more is of importance in 

 practically every timber producing area on this continent. East- 

 ern North America contains twelve species, while the remaining 

 members of the group inhabit the west. 



For the most part, each species of pine has a definite number 

 of leaves per cluster. The eastern white pine, common throughout 

 the Northeast, has five needles in a bundle, the red pine has two, 

 and the pitch pine has three. In most case where two species 

 have the same leaf number, other readily recognizable criteria 

 are available for exact determination. For example, the jack 

 pine and red pine both have two-needled clusters, but the red 



