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 leaves 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, 1n 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 
1Remarkable variations occur in the Reis Ancien 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, 
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