=Mouse-Ear Hawkweed.= _Hieracium Pilosella_ L. Flowers yellow; achenes jet black, oblong, straight or curved, apex truncate, base abruptly pointed, cylindrical or narrowly oval, the sides bearing 10 narrow vertical ridges. Introduced from Europe. The achenes very closely resemble those of the orange hawkweed. It doesn't matter much, for the habits are the same, and one is about as noxious as the other. Introduced from Europe. [Illustration: Fig. 202.] =Elecampane.= _Inula Helenium_ L. Flowers yellow; achenes light brown, straight or curved, linear, flattened, 4-5 mm. long, 4 sided with 5-8 obscure vertical ridges on each side, apex concave, the margin bearing a circle of short stiff bristles, the remains of longer ones. Introduced from Europe. Not common. [Illustration: Fig. 203.] =Marsh Elder.= _Iva xanthiifolia_ (Fresen.) Nutt. Achenes various shades of brown to black, flattened or rhombic in section, obovoid, 1.5-2 mm. long, longitudinally, striate with fine lines. Native to the upper peninsula of Michigan where it most likely was at one time introduced from the west. It has not been found in the lower peninsula, probably because it had no means of coming across Lake Michigan. [Illustration: Fig. 204.] =Wild Lettuce.= _Lactuca Canadensis_ L. Flowers yellow; achenes black or nearly so, flattened, oval, bearing 3 ribs, the lateral ones sometimes double, the middle one slender, surface abounding in minute transverse ridges as seen under a lens, the remains of a beak sometimes remaining. Native of this country. Other species of Lettuce are more or less troublesome. [Illustration: Fig. 205.] =Prickly Lettuce.= _Lactuca virosa_ L. For many years erroneously called _Lactuca scariola_. Flowers yellow; achenes dull, dark brown, mottled with black, flattened, bearing 5-7 rough, vertical ridges, interspersed by as many smaller ones; oblong, obovate, widest toward the tapering apex. 3-3.5 mm. long. Some of the leaves turn one edge up and the other down. Introduced from Europe and has proved itself a remarkable traveller. [Illustration: Fig. 206.] =Fall Dandelion.= _Leontodon autumnalis_ L. Flowers yellow; achenes light brown, linear, with 5 broad, rounded ribs; achene 4-6.5 mm. long, straight or curved, the outer traversed, with low transverse ridges. Introduced from Europe. [Illustration: Fig. 207.] =Black-eyed Susan. Yellow Daisy.= _Rudbeckia hirta_ L. Achene purple-brown to black, slightly tapering from base to apex 1.5-1.8 mm. long, base abruptly pointed, apex truncate, in cross section nearly square, having 5-7 slender vertical ridges on each side besides a larger one at each of the four corners. Widely distributed in meadows and pastures. [Illustration: Fig. 208.]