494 



WEED FLORA OF IOWA 



#* 



Fig. 371. Seeds of Burdock (Arctium lappa), a, a side view of one of the inner 

 achenes of a bur ; b, showing the inner surface of a curved, outer achene, 

 and exhibiting the character of the apex, both enlarged ; c, a group show- 

 ing natural size. 



(After Hillman, Bull. Nev. Agr. Exp. Sta.) 



Tall Thistle (Cirsium altissimum Willd.). 



Achenes lanceolate-obovate, tapering toward lower end, and some- 

 what narrowed toward the apex, wider in the middle, one-eighth in. 

 in length ; width one-twelfth in. ; dull brown or grayish excepting 

 light colored ring at upper end; numerous fine ridges; apex con- 

 cave, with the remnant of corolla tube projecting from the center; 

 color uniform; not marked by light and dark areas as the bull 

 thistle. 



& dr 



Fig. 372A Fig. 373B 



Fig. 372. Seeds of Thistles. A. Different views of Canada Thistle (Cirsium 



arvense). B. Bull Thistle (Cirsium lanceolatum) . 



(Drawings by Charlotte M. King.) 



Canada Thistle (Cirsium arvense (L.) Scop.). 



Achene lanceolate, narrowed at lower end, tapering from some- 

 what thickened top, one-twelfth to one-eighth in. long; the cup- 

 shaped top with a projecting conical portion, straight or slightly 

 curved; marked with longitudinal dark lines or furrows; apex 

 with a light colored border, giving appearance of a ring. Found in 

 seed of small grains, clovers and grasses. 



