THE CLASSIFICATION OF FOSSIL PLANTS 
The gymnosperms are best known to us by the conifers, 
to which belong the pines, hemlocks, spruces, cedars, 
and the host of other evergreen trees which grow all 
over the world. 
A group which is probably related to the conifers, but 
which became extinct long ago, is the cordaitales. They 
had large shafts and tufts of needle-like leaves of enor¬ 
mous size. Some of the leaves or needles were more than 
a yard long and two inches wide. 
The most highly developed forms of plant life are 
the angiosperms. The great majority of the familiar 
plants of today belong to this group, including all the 
foliage-bearing trees, the wild flowers, grasses, palms, 
shrubs, and innumerable others. The angiosperms are 
also divided into two groups, the monocotyledons and the 
dicotyledons, according to whether the seedling begins 
with one leaf, as in the monocotyledons, or with two 
leaves as in the dicotyledons. Most monocotyledons have 
long narrow leaves with parallel venation, as in the 
grasses or lilies, while most dicotyledons have complicated 
leaves with a midrib from which secondary veins spread, 
as in nearly all trees and shrubs and many of the flower¬ 
ing plants. 
Such a classification of plants as this, we call a biologi¬ 
cal one; it takes into account only their relations to each 
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