174 



AGRONOMY 



Oxeye daisy (Chrysanthemum leucanthemum). The large 

 white flowers of this species, universally known as daisies or 

 marguerites, are sufficient to identify it. It is a perennial, 

 spreading rapidly by means of its many small seeds, and be- 

 comes a bad weed in meadows and pastures, crowding out the 



rightful tenants of 

 the soil. It is some- 

 times known as 

 whiteweed. The 

 yellow daisy (Rud- 

 beckia hirta), also 

 common in fields 

 and meadows, is a 

 native species. 



Canada thistle 

 (Cnicus arvemis). 

 Many other spe- 

 cies of thistle are 

 confused with this 

 much-dreaded plant, 

 which, in spite of 

 the name it bears, 

 is an Old World 

 species, and not a 

 native of this con- 

 tinent. It may be 

 known by its very 

 prickly stems and leaves and its pale lavender blossoms of 

 small size. Owing to the fact that its rootstock is widely 

 creeping and deep in the earth, it is very difficult to eradicate 

 when once established. The plant has two kinds of blossoms, 

 those on some specimens being completely sterile. This has 

 given the impression in some sections that the plant does not 

 ripen good seeds in parts of its range. 



Photograph from American Steel and Wire Co. 



FIG. 123. A plant of wild mustard 

 This species is especially harmful in grainfields 



