A SEED KEY TO COMMON WEEDS 355 



apex; ten ribbed, the ribs being composed of diverging scales; 

 beak slender and from twenty to thirty mm. long. 0., fairly 

 common. Introduced from Europe. 



109. Tragopogon pratensis L. L., 10 — 15 mm. without pap- 

 pus; 12 — 25 with pappus. W., 1.4 — 2 mm. Color and shape, 

 almost identical with Tragopogon porrifolius. 0.. common in 

 rocky fields. Introduced from Europe. 



110. Taraxacum officinale Weber. Common Dandelion. L., 

 3. — 1.5 mm. without the style. W., .8 — 1.2 mm. C, straw- 

 colored or dark reddish brown. S., oblanceolate with twelve 

 to fourteen longitudinal ridges composed of barblike projections 

 pointed toward the apical end, near which they are clustered ; 

 beak in two parts, one short and thick and the other two or 

 three times the length of the achene. 0., very common espe- 

 cially in grass seeds. Naturalized from Europe. 



111. Sanchus oleraceus L. Common Sow Thistle. L.. 2.8 — 

 3.1 mm. W., 1. — 1.2 mm. C, straw-colored to reddish brown. 

 S., flattened oval with nine to fourteen fine longitudinal ridges ; 

 both ends rather abruptly terminated; with transverse wrinkles. 

 0., rather common in many farm seeds. Introduced from 

 Europe. 



112. Sonchus asper (L.) Hill. Spiny-leaved Sow Thistle. L.. 

 2.2—3.2 mm. W., .8—1.2 mm. C, dull reddish brown. S., 

 flattened oval sometimes with a slight wing; sometimes spindle-, 

 shaped ; with three to five longitudinal ridges on each face. 0., 

 rather common. Introduced from Europe. 



113. Lactuca scariola L. Prickly Lettuce. L., 3. — 3.8 mm. 

 W., .7 — 1 mm. C, dull brown and slightly mottled. S., spindle- 

 shaped, slightly broader towards the apical end, with five to 

 seven vertical ridges. 0., spreading rapidly and becoming quite 

 common. Introduced from Europe. 



114. Lactuca canadensis L. "Wild Lettuce or Horseweed. L., 

 3.3 — 4.8 mm. without the style. W.. 1.5—2.2 mm. C, dusty 

 black. S., flattened oval with three prominent ridges on each 

 face ; has the appearance of a winged seed ; beak quite persistent. 

 0., very common, and often troublesome. Native. 



115. Lactuca spkata (Lam.) Hitchc. L.. 3.5 — 5.2 mm. W.. 

 1. — 2.2 mm. C, dark brown. S., flat and irregularly oval with 

 from ten to sixteen ridges. 0., not particularly common. 

 Native. 



