640 WEED FLORA OF IOWA 



weeds have not prominent dissemination mechanisms but are trans- 

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

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

 of in^pure seed from agricultural seed necessitates the re^eognition 

 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. 



