narrow ridge about the margin.
About 1.7 mm. long. Introduced from Europe. Seldom troublesome in
Michigan.

[Illustration: Fig. 182.]

=May-weed. Dog's-Fennel.= _Anthemis Cotula_ L. Outer flowers white;
achenes straw color to light brown, obovoid (large end uppermost) to
oblong, circular in outline, 1.3-1.8 mm. long, with 10 warty ribs.
Introduced from Europe. Old roads and waste places.

[Illustration: Fig. 183.]

=Great Burdock.= _Arctium Lappa._ So far as I have seen the achenes of
this species, when compared with A. minus, are darker colored, rather
longer, the ribs more distinct.

=Smaller Burdock.= _Arctium minus_ Beruh. Possibly only a variety of _A.
Lappa_ L., but the prevailing plant in central Michigan. I see no way of
distinguishing the achenes of one from the other; but it makes little
difference as one burdock is as bad as another.

Flowers purple; achenes dull brown, often spotted with black, straight
or curved, slightly flattened, oblong-prismatic with 3-5 narrowly ridged
angles, and occasionally other smaller ridges, 4.5-6 mm. long.
Introduced from Europe.

[Illustration: Fig. 184.]

=Biennial Wormwood.= _Artemisia biennis_ Willd. Achenes dark brown,
smooth, somewhat flattened, 3-4 angled, obovate, narrowed at the base
.8-1.3 mm. long. Native in the northwestern United States and introduced
east with grass seeds. Moist land.

[Illustration: Fig. 185.]

=Smaller Bur-Marigold.= _Bidens cernua_ L. Flowers yellow; achenes 4-6
mm. long, dull brown, the awns lighter, flattened, 4-angled,
wedge-shaped, awns 2-4, barbed downward as also are the ribs. Native of
this country. Low lands.

[Illustration: Fig. 186.]

=Purple-stemmed Swamp Beggar-ticks.= _Bidens connata_ Muhl. Flowers
orange; achenes brown, wedge-shaped or obovate, hairy, tubercled,
flattened, 4-angled, 4-toothed, 4-6 mm. long, achenes and teeth
downwardly barbed. Swamps, common.

[Illustration: Fig. 187.]

=Beggar-ticks.= _Bidens frondosa_ L. Achenes dull brown, tubercled, much
flattened, obovate or oval, 6-12 mm. long, awns usually 2, spreading
barbed downward. Low lands.

[Illustration: Fig. 188.]

=Star Thistle.= _Centaurea solstitialis_ L. Achene cream white to
mottled brown, flattened, oval about 2 mm. long; scar of attachment in a
notch of one edge above the rounded base, apex truncate with a small
tubercle in the middle. Found in seeds of alfalfa. A ragged plant from
Europe.

[Illustration: Fig. 189.]

=Ox-eye Daisy