A SEED KEY TO COMMON WEEDS 365 



1. Not triangular in cross section or shining black. 



2. With numerous hooked terminal appendages 



Agrimonia striata Michx. 45 



2. Without terminal appendages but with a wing (fig. XXII) 



Asclepias syriaca L. 62 



I. 6 to 7 mm. long. 

 II. Spindle shaped with a deep groove up one side, twice as long 



as broad (fig. XXIII) Bromus secaiinus L. 11 



II. Not spindle shaped or with but one deep longitudinal groove. 



1. Triangular in cross section, shining black 



Polygonum scandens Michx. 20 



1. Not triangular in cross section. 

 2. With terminal spines or prickles. 



:'.. With not more than 4 awns or prickles. 



4. With 4 awns, 4 angles, faces slightly concave 



Bidens cernua L. 94 



4. With not more than 3 awns, usually 2, faces strongly 



1-nerved (fig. XXIX) Bidens frondosa L. 



3. With more than 4 terminal prickles usually hooked 



Agrimonia striata Michx. 45 



2. Without terminal spines or prickles. 



"3. Seeds winged (fig. XXII) Asclepias syriaca L. 62 



3. Seeds not winged. 



4. Uniform rusty brown, not over 1.4 mm. wide (fig. 



XVII) Prcnanthes alba L. 116 



4. Not uniform, rusty red. 

 5. Quite pronouncedly 4-faced, angles nearly equal.. 



Heliopsis helianthoides L. Sweet 90 



5. Not pronouncedly 4-faced or equally angled, usually 

 mottled in color. 

 6. Usually with 1 or more longitudinal striations 



quite angular (fig. IV) . . . .Arctium minus Berh. 103 

 6. Without longitudinal striations, not angular. . . . 



Helianthus divaricatus L. 92 



I. 5 to 6 mm. long. 

 II. At least twice as long as broad. 

 1. With long terminal awns. 



2. With not more than 3, usually 2 straight awns (fig. 



XXIX) Bidens frondosa L. 93 



2. With 4 awns, 4-angled Bidens cernua L. 94 



1. Without long terminal awns. 



2. Less than 1 mm. thick, curved with from 10 to 16 longi- 

 tudinal ridges, dark (fig. Ill) 



Lactuca spicata (Lam.) Hitchc. 115 



2. More than 1 mm. thick. 



3. Uniformly rusty red or gold-brown, less than 1.5 mm. 



broad, without a deep groove (fig. XVII) 



Prenanthes alba L. 116- 



