A SEED KEY TO COMMON WEEDS 369 



2. Surface not shining. 



3. Surface smooth, not hairy or with longitudinal lines. 

 4. More than 1.2 mm. wide, not reddish or tan. 



5. Light straw-colored (fig. XIX) 



Cirsium lanceolatum L. Hill. 104 



5. Dark-colored Helianthus divaricatus L. 92 



4. Less than 1.2 mm. wide, reddish (fig. VIII) 



Cirsium arvense L. Scop. 105 



3. SuPface ridged or hairy, not smooth. 

 4. Less than 1 mm. hroad. 

 5. Pronouncedly flattened. 



6. Very sharp attenuate at apex, dull brown 



Lactuca scariola L. 113 



6. Not sharply attenuate at apex. 



7. Distinctly reddish with fine longitudinal ridges 



Sonchus oleraccus L. Ill 



7. Brown, with comparatively heavy longitudinal 



ridges (fig. XXX) Daucus Carota L. 61 



5. Not pronouncedly flattened. 

 6. Square in cross section. 



7. Sharply pointed at base, very slender 



Eupatorium purpureum L. 81 



7. Not sharply pointed at base or slender 



Dipsacus sylvestris Huds. 80 



6. Not square in cross section. 



7. Very prominently 6- or 7-ridged, curved, usually 

 greenish, piano- or concavo-convex (fig. XXX) 



Daucus Carota L. 61 



7. Not prominently 6- or 7-ridged or curved. 



8. Light brown, broadest toward apex 



Senecio vulgaris L. 102 



8. Dark brown, broadest toward middle 



Erechtites hieracifolia (L.) Raf. 101 



8. Silvery or dark gray, broadest toward base 



(fig. XVIII) Tussilago Farfara L. 100 



4. More than 1 mm. broad. 



5. Surface not pronouncedly ridged. 



6. Very light colored, some faintly marked with 



dark (fig. XIX) . . . .Cirsium lanceolatum L. Hill 104 

 6. Not light colored. 

 7. Quite angular, mottled in transverse lines (fig. 



IX) Arctium minus Berh. 103 



7. Not angular, mottled longitudinally 



Helianthus divaricatus L. 92 



5. Surface conspicuously ridged. 

 6. Distinctly flattened. 



7. Black, winged with 1 to 2 ridges on each face 



(fig. VI) Lactuca canadensis L. 114 



24 



