ger, 1.5-2.5 mm.
long slightly flattened, with edges acute, very variable in shape, oval
oblong, rhomboidal, surface minutely roughened and dull, but wholly
without ridge or lines as in P. major. Native of this country. Lower end
of leaf-stalk red, and not clear green as in P. major. A vile pest in
clover fields.

MADDER FAMILY.

[Illustration: Fig. 176.]

=Blue Field Madder.= _Sherardia arvensis_ L. The parts often called
seeds are in reality the half-fruits ripened, each one bearing at the
apex three, white, pointed, persistent calyx lobes, the inner face
showing a vertical groove, and in some of the fruits the calyx is broken
off. Surface dull brown, clothed with small white hairs, obovoid, 2-2.5
mm. long. Introduced from Europe, not often found in the northern
states.

TEASEL FAMILY. DIPSACACEAE.

[Illustration: Fig. 177.]

=Wild Teasel.= _Dipsacus sylvestris_ Huds. Achene brown, minutely hairy,
4 mm. long, oblong, square in cross-section, with four vertical ribs on
the angles and four on the sides. Seed suspended, anatropous, supplied
with endosperm. Introduced from Europe. A weed requiring two years from
seed to seeding.

COMPOSITE FAMILY. COMPOSITAE.

[Illustration: Fig. 178.]

=Yarrow. Milfoil.= _Achillea Millefolium_ L. Flowers white; achenes
white to gray, finely striate lengthwise, flattened, oblong, tapering at
the lower end, straight or curved. 2-2.3 long. Most likely introduced
from Europe.

[Illustration: Fig. 179.]

=Ragweed.= _Ambrosia artemisiifolia_ L. Achenes hard, straw-colored to
light brown or black, top-shaped, broadly oval, 2.5-3 mm. long, besides
the beak 1.5 mm. long, the sides irregularly ridged vertically, with
5-10 short teeth at the apex. Sometimes the hard covering is removed by
a clover huller, exposing the naked seed. Native of the U. S.

[Illustration: Fig. 180.]

=Great Ragweed.= _Ambrosia trifida_ L. Achenes hard, brown, more or less
mottled, top-shaped, 7-8 mm. besides the stout beak 2-3 mm. long, sides
with 5 stout ridges terminating in 5 short teeth. Native to the United
States. River bottoms, low land, sometimes 15 ft. high.

[Illustration: Fig. 181.]

=Corn Camomile=. _Anthemis arvensis_ L. Achenes very variable, creamy
white to light brown, oblong, wedge-shaped in outline, circular to
four-angled in cross-section, more or less ribbed lengthwise, a
ripple-shaped scar at the narrow end; apex truncate with a minute
projection in the center, often with a