370 IOWA ACADEMY OF SCIENCE 



7. Dark brown with 10-16 ridges irregularly oval 



(fig. Ill) Lactuca spicata (Lam.) Hitchc. 115 



6. Not distinctly flattened. 



7. Plano-convex or concavo-convex, ridges spiny, 



wide (fig. XXX) Daucus Carota L. 61 



7. Square in cross section with 2 grooves on each 



face (fig. XIII) Dipsacus sylvestris Huds. 80 



7. Not square in cross section, very prominently 

 6- or 7-ridged, ridges not spiny, reddish (fig. 



XXI) Carum Carvi L. 60 



II. Not twice as long as broad. 

 1. Triangular in cross section. 

 2. Black. 



3. Shining black, over 3.5 mm Polygonum scanclens L. 20 



3. Dull black, less than 3.5 mm. (fig. XXXV) 



Polygonum Convolvulus L. 19 



2. Not black. 



3. Prominently transversely ridged with black or darker 



lines Setaria glauca ( L. ) Beauv. 4 



3. Surface not transversely striate, shining 



Echinochloa Crus-galli L. Beauv. 3 



1. Not triangular in cross section. 

 2. Black or nearly so. 

 3. Round and markedly shining. . .Polygonum Persicaria L. 17 

 3. Not round and not markedly shining. 

 4. Thin and wafer-like, usually winged. 



5. Nearly circular without longitudinal striations. . . . 



Laportea canadensis (L.) Gaud. 12 



5. Oval with 1 to 2 longitudinal striations on each face 



(fig. VI) Lactuca canadensis L. 114. 



4. Not thin or wafer-like or winged. 



5. One side covered with stiff prickles 



Lappula virginiana (L.) 66 



5. Not as above. 



6. Acuminate at one end, not pronouncedly ridged 



Helianthus divaricatus L. 92 



6. Not acuminate at one end. 



7. Surface covered with gray hairs 



Malva moschata L. 57 



7. Surface not covered with hairs. 



8. Nearly as thick as wide, surface with about 

 30 rows of short rounded projections, 



angular Agrostemma Githago L. 31 



8. Not nearly as thick as wide, surface with 



shallow pits somewhat kidney-shaped 



Datura Stramonium L. 73 



2. Not black or nearly so. 



3. Shining chestnut brown Polygonum virginianum L. 18 



3. Not shining chestnut brown. 



