a-pastoris_ (L.) Medic. _Bursa
Bursa-pastoris_ (L.) Britton. Flowers small, white; pods flat, nearly
triangular, about 4 mm. long. Seeds reddish yellow, granular, oblong,
slightly flattened, 1 mm. or less long. Each side usually bearing two
longitudinal grooves, separating the surface into three nearly equal
parts, these grooves indicating the position of the parts of the embryo.
When placed in water, a copious coat of transparent mucilage appears on
the surface. In Nevada and Colorado a great pest in fields of Alfalfa.

[Illustration: Fig. 88.]

=Hare's Ear.= _Conringia orientalis_ (L.) Dumort. Seeds brown, surface
checked off into minute irregular pits or patches; broad oval, 2-2.5 mm.
long, in section nearly circular, except two opposite slight grooves
near one side. Cotyledons incumbent. Introduced, not common.

[Illustration: Fig. 89.]

=Sand Rocket.= _Diplotaxis muralis_ (L.) DC. Flowers yellow, seeds
reddish yellow or reddish brown, broad oval, somewhat flattened.
Mucilaginous when wet. Introduced from Europe. A vigorous weed.

[Illustration: Fig. 90.]

=Worm-seed or Treacle Mustard.= _Erysimum cheiranthoides_ L. Flowers
yellow; seeds reddish yellow, smooth, dull, about 1.2 mm. long, ovoid or
oval, more or less flattened, varying much in shape; some of them acute,
rhombic or triangular, becoming mucilaginous when wet. Probably
introduced from Europe. If not already in some portions of the state, we
may at any time expect to find three other species of Erysimum. A
vigorous and prominent weed.

[Illustration: Fig. 91.]

=Apetalous Pepper-Grass.= _Lepidium apetalum_ Willd. Petals usually
wanting, sometimes 2 and minute; pods flat, nearly circular; seeds
reddish yellow, flattened, ovate, 1.5-1.8 mm. long, or more exactly,
nearly straight on one side and roundish on the other. Mucilaginous
when wet. Cotyledons incumbent. When well developed in open places it
becomes a tumble weed. Apparently naturalized from Europe.

[Illustration: Fig. 92.]

=Field Pepper-Grass or Cow Cress.= _Lepidium campestre_ (L.) R. Br.
Petals white; pods flat, nearly circular; seeds dull, dark brown,
obovoid, with base acute, more or less flattened on three sides, 2-2.5
mm. long. Mucilaginous when wet. Cotyledons incumbent. Naturalized from
Europe.

[Illustration: Fig. 93.]

=Hoary Cress.= _Lepidium Draba_ L. Seed reddish brown, surface slightly
uneven, slightly flattened, oval to broad oval, 2-2.3 mm. long, usually
with two sli