78 WEEDS OF THE FARM AND GARDEN 



of foxglove, pansy, and a great deal of velvet grass and 

 much Canada thistle, besides numerous other plants 

 which are carefully cultivated in the eastern states for 

 ornamental purposes. 



Dr. Gray has somewhere said that most of the trouble- 

 some weeds of western Europe originated in the East. 

 It is certainly true that as conditions are prepared, weeds 

 spring into existence. Such plants as are best adapted to 

 stand adverse conditions assert themselves and become 

 the pests of the farmer. 



Annual weeds seem to have a better chance to adapt 

 themselves than perennial. Of the annual weeds we may 

 mention the purslane, Jimson weed and Indian mallow. 



It does not require much botanical knowledge to 

 recognize the similarity of the flora of our "great plains." 

 Many of the prairie plants are common from Texas to 

 Manitoba. The compass plant (Silphium laciniatum), 

 buffalo bur (Solatium rostratum), common sunflower 

 (Helianthus annuus), etc., are alike common to the prai- 

 ries of Texas, Kansas, Nebraska and the Dakotas. 



It is remarkable how rapidly European weeds have 

 spread in parts of South America. In the neighborhood 

 Df Buenos Ayres, are found bur clover (Medicago hispida), 

 its allies, and a composite (Silybum marianum), which has 

 also become noted as a pest in California ; Cynara cardun- 

 cidus covers the pampas for miles. The European 

 grasses, like the perennial rye grass (Lolium perenne), 

 squirrel grass (Hordeum murinum) and other wild bar- 

 leys (H. pratense) have rapidly taken the place of native 

 grasses. The interesting observation has been made in 

 South America and Australia, that indigenous (native) 

 plants have been crowded out by closely related European 

 species. In Australia, common sow thistle (Sonchus 

 oleraceus), a truly cosmopolitan weed, has established 

 itself in low grounds near streams and has crowded out 

 a native species of sonchus. It is possible that some of 



