2 BULLETIN 460, U. S. DEPARTMENT OF AGRICULTURE. 



reader will also find full information in Bulletin 207 regarding the 

 class and family relationship of the pines to other coniferous trees 

 of the Rocky Mountains. 



GENERIC CHARACTERISTICS OF PINES. 



All of the pines are evergreen trees, their branches being more or 

 less thickly clothed with clusters of leaves which are needlelike and 

 borne in bundles or fascicles of 1, 2, 3, 4, or 5. 1 When the leaves 

 first appear, they have a basal sheath of scales, in some cases very 

 thin and in others thicker and stiff. In some pines these scales are 

 retained until the leaves die, while in others they are shed when the 

 leaves become fully grown. The leaves vary in length from about 

 1 to 15 inches. The juvenile or primordial form of leaf borne on the 

 first shoot of seedling pines differs from the adult form by being 

 single, this form soon being followed by adult or true foliage 

 leaves. Seed-leaves (cotyledons) of pines, the first foliar organs 

 produced when the seed germinates, are needle-shaped and from 



3 to 15 in number. The leaAes of pines vary from cylindrical, as in 

 the single-leafed species, and half-round, as in two-leafed pines, to 

 a triangular or three-edged leaf in the 3- to 5-leafed species. The 

 edges of the leaves of some pines are provided with minute teeth, 

 while those of others are smooth. The color of the leaves ranges 

 from a blue or silvery green to a deep yellow-green, the surfaces 

 bearing lines of minute pores or stomata. In cross section the 

 leaves of pines show from 2 to 14 minute resin ducts, the position 

 and number of which vary in different species. A new set of leaves 

 is formed each year on the young twigs. The leaves produced each 

 season may remain on the tree from 2 to 6 or 8 years, during which 

 they maintain their green color and vegetative activity. When a set 

 of new leaves is being formed at the ends of the new twigs, the oldest 

 set of leaves, situated farther back on the branches, dies and falls to 

 the ground. The winter buds of pines are variable in form and in 

 size, and all are covered by fringed or papery-margined overlapping 

 scales. The component scales each protect a tiny bud, which, when 

 the main bud unfolds in the spring, develops into a fascicle of 

 leaves or, in some cases, into a female flower. 



The flowers of the pines are male and female, borne usually on 

 different branches of the same tree. Male flowers, which produce 

 pollen, are short, oval, and budlike, or long cylindrical bodies, clus- 

 tered at the ends of mature leafy branches. In color they are bright 



1 Remarkable variations occur in the generally regular number of leaves borne by the 

 2- 3- 4- and 5-leafed pines, a 2- or 3-leafed species occasionally or frequently having a 

 number of 3- and 4-leafed fascicles, while the 4- and 5-leafed pines may have some fasci- 

 cles with 5, 6, or 7 leaves. Whether or not these variations represent gradual transitions 

 from one type to a different type of foliar habit can not be affirmed at present. 



