A SEED KEY TO COMMON WEEDS 367 



3. Surface with longitudinal striations. 

 4. Fruit very thin but not narrow. 

 5. Broader towards apex, winged, black with usually 

 but one longitudinal ridge on each face (fig. VI) 



Lactuca canadensis L. 114 



5. Broadest toward base or near center, brown, with 



two or more longitudinal ridges (fig. Ill) 



Lactuca spicata Lam. Hitchc. 115 



4. Fruit not thin, nearly as thick as broad. 

 5. More than 1.5 mm. broad. 



6. Quite pronouncedly 4-faced and uniform in color 



Heliopsis helianthoides L. Sweet. 90 



6. Not pronouncedly 4-faced and usually mottled in color. 

 7. Usually with 1 or more longitudinal striations, 

 angular and mottled transversely (fig. IV) 



Arctium minus Berh. 103 



7. Usually without longitudinal striations, not 

 angular and if mottled, mottled longitudinally 



Helianthus divaricatus L. 92 



5. Less than 1.5 mm. broad. 



6. Quite pronouncedly curved, tapering at both ends 

 with about 6 light longitudinal striations (fig. 



XXI) •. Carum Carvi L. 60 



6. Not pronouncedly curved or tapering at each end. 



7. With two deep grooves or three ridges on a 



side, comparatively short, quite 4-sided (fig. 



XIII) Dipsacus sylvestris Ruds. 80 



7. Without deep grooves or with more than 3 ridges 

 on a side. 

 8. Distinctly reddish brown, with 17-20 fine lon- 

 gitudinal striations (fig. XVII) 



Prenanthes alba L. 116 



8. Not reddish brown, with 20-30 fine longitudi- 

 nal striations Inula Helenium L. 85 



II. Not twice as long as broad. 



1. Triangular in cross section, shining black 



Polygonum scandens Michx. 20 



1. Not triangular in cross section. 



2. With numerous terminal appendages or spines 



Ambrosia artemisiifoUa L. 86 



2. Without numerous terminal appendages. 

 3. Surface shining. 



4. Rich chestnut brown, oval. .Polygonum virginianum L. 18 

 4. Grayish white, obliquely truncate at base (fig. XXXI) 



Centaurea Cyayius L. 106 



3. Surface not shining. 



4. Fruit globular, white Rhus Toxicodendron L. 53 



4. Fruit not globular nor white. 



