WEED MIGRATION 



691 



in a few places where tillage was not good; but in nearly every 

 case these perennial weeds disappeared from the cultivated fields 

 which thereupon became occupied by a large number of native 

 annual weeds like the greater ragweed {Ambrosia trifida), Spanish 

 needle {Bidens frondosa, B. discoidea) and smartweed {Polygonum 

 sp.), a few hardy perennial weeds like milkweed {Asclepias 

 syriaca), morning-glory {Convolvulus sepium), artichoke {Helian- 

 thus tuberosus) and meadow sunflower {Ilelianthus grosseserratus) . 

 Such annual or winter annual weeds as scjuirrel-tail grass {Hordeum 

 jubatum), peppergrass {Lepid/ktm apetalum) began to compete 

 with a host of European and other exntie wppds like lamb's quarters 

 ( Chenopodmm album), persiearia {Polygonum persicaria) , purslane 

 {Portulaca oleracea), foxtail {Setaria glauca, 8. viridis) and, later, 

 crab grass {Digitaria sanguinalis and D. humifusa). In grain 



FlQ. 533. Greater Ragweed (.Ambrosia ti'ft'm. 'I'l is weed rai'idlv occupief- 



cultivated ground. 

 (Vasey, U. S. Dept. Agr.) 



