I l IOWA ACADEMY OF SCIENCE 



or yellowish brown, s.. obovate or ovate with a slight curved 

 beak at the apical end and a narrow wing around the edge; 

 base set obliquely to the longitudinal axis of the seed: one side 

 convex, the other nearly flat; thin. (>.. common in lowlands 

 and fields. Introduced from Europe. 



Lepidium rude-rale L. Pepper Wort, Pepper Crass. L. 

 1.4 — l.S mm. \Y. .6 — 1. mm. C. tan to yellow-brown. S.. 

 obovate, narrowly winged; narrower at the apical end thus 

 differing from Arabis laevigata; with a groove running down 

 each side Prom the scar. C. common in clovers and grasses. 

 [ntroduced from Europe. 



39. Capsella Bursa-pastoris. L. Medic. Sheperd's Purse 

 I. 5 —1.2 mm. W. .2 — .8 mm. C, yellow to reddish brown. 

 S.j flattened oblong with a longitudinal groove running in a 

 loop from the base for nearly the whole length of the seed. 

 0., common in white, alsike and red clovers, also in blue grass, 

 a pest in alfalfa. Introduced from Europe. 



40. Brassica nigra. (L) Koch. Black Mustard. L. 1. — 1.8 



mm. AY. 1. — 1.6 mm. ('.. dark reddish brown with a net- 

 work of lighter lines, s.. only slightly flattened spherical^; 

 sometimes a trifle angular: surface pitted and covered with a 

 network of ridges. <).. found in clovers and grass seeds. In- 

 troduced from Europe. 



41. Sisymbrium officinale (L) Scop. Hedge Mustard. L. 

 .8 — 1.5 mm. W. .3 — .8 mm. ('.. tan or yellowish, greenish 

 brown. S., quite irregularly oval to oblong, usually more blunt 

 at the apical end and tapering at the base: a curving line 

 from the scar down one side follows the outline of the cotyle- 

 dons, 0., a rather common weed. Introduced from Europe, 



42. Barbarea vulgaris. R. Br. Common Wild Mustard. L. 



.8 — 1.7 mm. W. .6 — 1.2 mm. C. light brown shining slight- 

 ly under the microscope. S., flattened oval, irregular and with 

 a distinct elevation at the sear: surface sparingly covered with 

 a network o\ fine ridges or pits. Differs from Brassica nigra 

 in being lighter in color, flatter and in having less pronounced 

 ridges or pits. 0., common in fields and gardens and in many 

 seeds. Introduced from Europe. 



43. Arabis laevigata Muhl Poir. Rock Cress. L. 1.5 — 1.8 

 mm. W. .8 — 1. mm. C. tan to yellow-brown. S., flattened 

 oval to oblong with a small hook at the blunt end; with a 



