69 



lumbermen and the public since the American Forests began to be 

 exploited. Until recently more pine lumber has been produced an- 

 nually in the United States than all other kinds of lumber com- 

 bined. The lumber-producing pine trees have played a very impor- 

 tant role in our economic and industrial development. The Pines 

 are distinguished commercially into two classes, Soft Pines and 

 Hard Pines. In the United States there are 12 species of Soft Pine, 

 and 22 species of Hard Pine. The White Pine is the sole eastern 

 representative of the Soft Pines, while the Hard Pines have 12 repre- 

 sentatives in the eastern and southern United States. 



The Pines have three kinds of leaves : seed, primary, and secondary 

 leaves. The primary leaves soon disappear and are seldom seen ex- 

 cept on seedlings. The secondary leaves occur singly or in clusters 

 of 2 to 5 and often have a persistent or deciduous sheath surrounding 

 them at the base. They are semi-circular or triangular in cross- 

 section, depending upon the number which occur in a cluster. The 

 flowers usually appear in spring. The staminate are borne at the 

 base of the season's growth in clusters and produce enormous quanti- 

 ties of sulphur-like pollen. The pistillate occur near the terminal 

 part of the new shoot or laterally along it, solitary or in whorls 

 of 2-5 or more. Prior to pollination they normally stand erect but 

 after this process has been completed they begin to droop. The 

 wind is the chief agent of pollination. Fertilization takes place 

 about 13 months after pollination. The result of these processes is 

 usually a cone which matures at the end of the second or sometimes 

 the third season. The cones are composed of numerous scales at the 

 base of which the seeds are produced in pairs. 



KEY TO THE SPECIES. 



Page. 



1. Leaves 5 in a sheath, slender, with 1 fibro-vascular bundle P. Strobus 70 



1. Leaves fewer than 5 in a sheath, usually stout, with 2 fibro-vascular bundles, 2 



2. Leaves 3 in a sheath, P. rigida 71 



2. Leaves 2 in a sheath 3 



3. Leaves 5-6 inches long; cones subterminal, scales unarmed, P. flesinosa 72 



3. Leaves less than 5 inches long; cones lateral, scales armed with spines or prickles, .4 



4. Cones 2h-3l inches long, armed with stout spines; leaves very sharp-pointed and 



stiff, P. pungens 73 



4. Cones 3 inches or less in length, armed with prickles; leaves slender to slightly stiff, .5 



5. Leaves slender, straight, occasionally 3 in a sheath, 4 inches long or less, P. echinata 74 



5. Leaves stout, twisted, li-3| inches long, 6 



6. Twigs smooth, greenish-purple to grayish-brown; cones at right angles to branch 



P. virginiana 75 



6. Twigs rough, dull grayish-yellow; cones pointing backward; bark of upper third of 



trunk reddish; European species, P. sylvestris 76 



i 



