e obtuse or bearing the
remains of the thin calyx. Introduced from Europe. Low wet places.

=Shore Knotweed.= _Polygonum littorale_ Link. So far as the achenes are
concerned, they are identical with those of P. aviculare above
described. Native of this country. On hard or thin places, especially
when newly graded.

[Illustration: Fig. 36.]

=Pennsylvania Persicaria=, _Polygonum Pennsylvanicum_ L. Achene shining,
jet-black, flattened, surface very slightly uneven and granular nearly
circular with a short abrupt apex, edge rounded, 2.5-3 mm. long, often
bearing the remains of the calyx. Native to this country. Occasional in
annual crops.

[Illustration: Fig. 37.]

=Lady's Thumb.= _Polygonum Persicaria_ L. Achene shining, jet-black,
surface finely uneven, much flattened with rounded edges or with 3
nearly equal concave faces, the edges faintly angled along the center,
broadly ovate, base obtuse or bearing a portion of the calyx, apex
abruptly pointed, 2-2.3 long. Introduced from Europe. Waste places and
stubble ground.

[Illustration: Fig. 38.]

=Climbing False Buckwheat.= _Polygonum scandens_ L. Achene black,
shining, in cross-section sides flat or concave, corners rounded,
obovate, in vertical outline sides rounded to an obtuse apex, from
rounded sides to base slightly concave, base acute, 3.5-4 mm. long when
freed from the persistent base of the calyx. Woods and shady places. Not
prominent as a weed.

[Illustration: Fig. 39.]

=Sorrel. Sour Dock.= _Rumex Acetosa_ L. Calyx-wings broadly ovate or
orbicular, heart-shaped 3.5-4.5 mm. long, achene shining, with 3 equal
sides, broadly oval, both ends abruptly pointed, the thin edges usually
lighter colored than the dark brown or black convex faces, 1.5-2 mm.
long. Introduced from Europe. Not common.

[Illustration: Fig. 40.]

=Sheep Sorrel.= _Rumex Acetosella_ L. Achenes usually closely covered by
dull reddish brown, finally roughened calyx, which is removed with
difficulty; achenes shining with 3 equal sides, broadly oval, the base
rounded, the apex abruptly pointed, sides convex, reddish brown or amber
color, corners obtuse, darker colored. Native of this country, though in
large part introduced from Europe. Very common in thin sandy meadows.

[Illustration: Fig. 41.]

=Narrow-leaved or Curled Dock.= _Rumex crispus_ L. Achene covered by 3
brown heart-shaped calyx-wings, which are 2.5-3.5 mm. long, each bearing
an ovoid, acute tubercle; one of them is 1.5 m