374 IOWA ACADEMY OF SCIENCE 



10. .5 mm. or less broad. 



11. Light brown, broadest toward the 



apex Senecio vulgaris L. 102 



11. Dark brown, broadest toward the mid- 

 dle. .ErecMites Meracifolia (L.) Raf. 101 

 10. Over .5 mm. broad. 



11. With pronounced lateral ridges. 

 12. With more than 5 prominent ridges, 

 not square in cross section, dark 

 surface with lighter ridges (fig. 



XXI) ! Carum Carvi L. 61 



12. With less than 5 prominent ridges, 

 somewhat square in cross section, 

 one face noticeably lighter and a 



light scar at hilum (fig. XI) 



Verbena hastata L. 69 



11. Without prominent lateral ridges... 



Cirsium . arvense (L».) Scop. 105 



II. Not twice as long as broad. 



1. Noticeably triangular or semi-circular in cross section. 

 2. Semi-circular in cross section. 



3. Surface smooth Echinochloa Cras-galli (L.) Beauv. 3 



3. Surface not smooth. 

 4. With lateral striations, usually over 2.5 mm. long (fig. 



XXXVII) Setaria glauca (L.) Beauv. 4 



4. With lateral and longitudinal striations, usually 2.5 



mm. long Setaria viridis (L.) Beauv. 5 



2. Not semi-circular in cross section but noticeably triangu- 

 lar. 

 3. Dull black, over 2.5 mm. long. .Polygonum Convolvulus L. 19 

 3. Brown or tan, usually under 2.5 mm. long. 

 4. Shining, abruptly attenuate at end, angles acute. 

 5. Sides and angles concave and dipping just back of 



apex (fig. XXXVI) Rumex crispus L. 13 



5. Sides and angles straight, apex more acuminate.. 



Rumex obtusifolius L. 14 



4. Not shining, angles somewhat rounded, unequally 3- 



sided Polygonum avicuJare L. 16 



1. Not noticeably triangular in cross section. 

 2. Thin and wafer-like. 

 3. White or light gray, obovoid. . . .Achillea millefolium L. 96 

 3. Not white or light gray. 

 4. Black or blackish. 



5. Shining, almost round Polygonum Persicaria L. 17 



5. Not shining. 



6. With a broad wing all around periphery 



Linaria vulgaris Hill. 76 





