THE GENERAL CHARACTERS OF SEED'S 



495 



Field Thistle (Cirsium discolor (Muhl.) Spreng.). 



Achenes obovate, inner edge nearly straight, outer curved, convex ; 

 one-seventh to one-sixth in. long, tapering from narrowed base 

 to apex, upper part longitudinally striated, slightly pigmented; 



Fig. 373. Seeds of Thistle. 3. Cirsium altissimum. 4. Cirsium discolor. 5. 



Cirsium undulatum. 6. Cirsium ioense, 



(Drawing by Charlotte M. King.) 



grayish, upper part yellowish for one-third length of the achene. 

 Found in seed of alfalfa and red clover. 



Iowa Thistle {Cirsium ioense (Pammel) Fernald). 



Achenes obovate, lanceolate, one side of seed straight, outer side 

 slightly convex, one-fifth to one-fourth in. long, one-twelfth to one- 

 sixteenth in. in width, gradually tapering from lower end toward 

 upper end, prominently widened just below the apex, marked by 

 longitudinal striations and dark areas, upper part yellowish, promi- 

 nent rim glossy; apex concave, with the prominent projecting rem- 

 nant of flower center. 



Bull Thistle (Cirsium lanceolatum (L.) Hill). 



Achene lanceolate, curved, tapering, in many cases somewhat 

 angular, one-eighth to one-sixth in. long; brownish, not darkly 

 striated, marked with definite grooves, upper part lighter, ringed, 

 also showing at center of concave apex ; apex with projecting point. 

 Found in red clover and in alfalfa seed. 



Wavy-leaved Thistle (Cirsium undulatum (Nutt.) Spreng.). 



Achene in general outline lanceolate, tapering from base, inner 

 edge slightly convex, several prominent ridges, light brown, not 

 pigmented; upper part yellowish; apex with prominent rim and 

 prominent remnant of corolla tube; achene slightly thicker than 

 that of C. discolor. Found in seeds of red clover and alfalfa. 



