340 IOWA ACADEMY OF SCIENCE 



brown. S., triangular in cross section with acute angles; 

 abruptly obtuse at the base and rather attenuate at the apex 

 (not as attenuate at the apex as Rumex obtusifolius). 0., the 

 commonest Rumex in farm seeds, found chiefly in blue grass, 

 orchard grass and red clover. Introduced from Europe. 



14. Rumex obtusifolius. L. Broad leaved or Bitter Dock. 

 L. 1.8 — 2.4 mm. W. .8 — 1.4 mm. C, light reddish brown 

 or tan and shining. S., triangular in cross section; rather at- 

 tenuate at the apex and more contracted at the base ; sides 

 convex or slightly so ; angles near the base slightly concave, 

 near the apex convex. 0., sometimes found in farm seeds. In- 

 troduced from Europe. 



15. Rumex Acetosella L. Field or sheep sorrel. L. 1.2 — 

 1.8 mm. W. .8 — 1.4 mm. C, shining reddish brown. S., 

 three-sided in cross section, abruptly tapering to a point at 

 the apex and rounded at the base; angles rounded and sides 

 convex. 0., common in red clover, orchard grass and timothy. 

 Native. 



16. Polygonum aviculare L. Knot Grass, Knot-weed. L. 

 1.8 — 2.4 mm. W. .8 — 1.4 mm. C, dull reddish brown. S., 

 unequally three-sided, tapering at the apex to a long acuminate 

 but at length rounded point; base moderately tapering to a 

 rounded point; angles rather abrupt and rounded; surface 

 finely granular in longitudinal striations. 0., of minor im- 

 portance as a field weed although often found as an adulter- 

 ant of red clover. Native. 



17. Polygonum Persiearia L. Lady's Thumb. L. 2. — 2.8 

 mm. W. 1.7 — 2. mm. C, shining jet black. S., broadly oval 

 or round with a short point at the apex and a short pro- 

 jection at the base; flattened, although the faces are more or 

 less concave. 0., common in various kinds of farm seeds 

 especially in red clover. Introduced from Europe. 



18. Polygonum rirginianum L. Virginia Knotweed. L. 

 3.4 — 4.4 mm. W. 1.8 — 2.4 mm. C, shining chestnut brown. 

 S., chestnut shaped but more attenuate at the base, oval in 

 general outline ; surface smooth and highly polished. 0., 

 common in low and waste grounds. Native. 



19. Polygonum Convolvulus L. Wild Buckwheat, Black 

 Bindweed. L. 2.5—3.5 mm. W. 1.8—2.3 mm. C, dull jet 



