g twigs very angular and bearing very large (6 to 9 in. long)
leaves. A very large (80 to 100 ft. high) tree, common in the
Mississippi valley, but found in western New England and often planted.

[Illustration: P. nigra.]

7. =Populus nigra=, L. (BLACK POPLAR.) Leaves rather large, deltoid,
pointed, serrate with glandular teeth, smooth on both sides even when
young. Leafstalk somewhat compressed. Buds very sticky. A very variable,
large (50 to 80 ft. high), rapidly growing tree with spreading branches.
Occasionally planted. From Europe.

[Illustration: P. balsamifera.]

8. =Populus balsamifera=, L. (BALSAM-POPLAR. TACAMAHAC. BALM OF GILEAD.)
Leaves very large, ovate, gradually acuminate, sometimes heart-shaped,
finely serrate, smooth, bright green and shining on both sides;
leafstalk nearly round; leaves in spring rich yellow. Branches ridged
below the leaves; buds large and covered with very fragrant resin. A
medium-sized tree, 40 to 70 ft. high, pyramidal in form. Wild in the
North and often cultivated.

Var. _candicans_, or Balm of Gilead, has larger and more or less
heart-shaped leaves (the larger figure in the cut).

CLASS II. GYMNOSPERMAE.

Plants in which the pistil is represented by an open scale instead of a
body with a closed ovary, as in Class I.

ORDER =XLI. CONIFERAE.= (PINE FAMILY.)

As far as the number of species is concerned, this is the largest order
of trees and shrubs of temperate and cold-temperate regions. The order
is of the greatest importance, both on account of the valuable timber it
furnishes and for its resinous secretions, turpentine and resin.

GENUS =93. PINUS.= (THE PINES.)

Leaves needle-shaped, 1 to 15 in. long, almost cylindric, 2, 3, or 5
together in clusters, with a sheath, more or less persistent, at the
base. Flowers monoecious, both staminate and pistillate in catkins,
usually insignificant and unnoticeable. In spring. Fruit a cone,
persistent and formed of more or less woody, overlapping scales.

* Leaves usually 5 together in bundles. (=A.=)

=A.= Leaves 6 in. or more long, glaucous green and very
pendulous 1.

=A.= Leaves under 4 in. long. (=B.=)

=B.= Cones over 10 in. long, on stalks 3 in. long,
pendulous when ripe 2.

=B.= Cones 4 to 10 in. long. (=C.=)

=C.= Scales of cones thin, unarmed