640 WEED FLORA OF IOWA 



weeds have not prominent dissemination mechanisms but are trans- 

 ferred with agricultural seeds, as carrot, buckhorn, dodder, sheep 

 sorrel, yellow trefoil, quack grass and pigeon grass. The separation 

 of impure seed from agricultural seed necessitates the recognition 

 by their morphological characters of obnoxious seeds. 



An economic consideration of dissemination of weed seeds and 

 their control involves (1) familiarity with the morphology of the 

 fruit and seed; (2) the limitation of the habitat in which the weed 

 is able to thrive; (3) recognition of the avenues and agents of dis- 

 tribution. 



