WEED MIGRATION 



729 



prickly lettuce (Lactuca scariola) and storksbill (Erodium cicu- 

 tarium). There are also such native weeds as bee-plant (Cleome 

 serrulata), wild liquorice (Glycyrrhiza lepidota), the squirrel-tail 

 grasses (Hordeum jubatum and H. caespitosum) , prickly lettuce 

 (Lactuca pulchella), pine-apple weed (Matricaria suaveolens) and 

 prickly poppy (Argemone platyceras) . In the Rocky mountain re- 

 gion, especially Colorado, many of the more recent introductions 

 are from Europe. Among these are the sweet clovers (Melilotus 

 alba and M. officinalis), black medick (Medicago denticulata) , 

 purslane (Portulaca oleracea) , dodder (Cuscuta arvensis and C. 



Fig. 551A I 



Pig. 551A II 



^6K 9 



Pig. 551A III Pig. 551A IV 



Fig. 5 51- A. Seeds scattered with agricultural seeds. I. Barnyard Grass 

 (Echinochloa crusgalli). II. Medicago denticulata, common in alfalfa 

 seed. II. Horehound (Marrubium vulgare) , a weed commonly scattered 

 with alfalfa seed. Common in the Great Basin country. IV. Wild Buck- 

 wheat or Bindweed (Polygonum convolvulus), commonly scattered with 

 grain seed. 



(All after Hillman.) 



epithymum) , foxtail (Setaria viridis) , storksbill (Erodium cicu- 

 tarium), Russian thistle (Salsola kali var. tenuifolia), vegetable 

 oyster (Tragopogon porrifolius), goat's beard (T. pratensis) and 

 lamb's quarters (CJicnopodiuyn album). A large number of native 

 plants have become weedy, such as marsh elder (Iva xanthifolia) , 



