VEGETATION OF MEADOWS AND PASTURES 61 



have stamens with long filaments, so that the anthers swing in 

 the air, and the plant is wind-pollinated. The pistillate flowers 

 have tufted stigmas, reddish purple in colour. 



Certain of these weeds are characteristic of particular manures. 

 It is found at Rothamsted that the Beaked Parsley is a prominent 

 weed when nitrate of soda has been used ; the Buttercup, the 



FIG. 21. Black Knapweed (Centaurea 

 nigra). 



FIG. 22. Salad Burnet (Poterium 

 Sanguisorba). 



Black Knapweed, Plantain, and Yarrow were characteristic of 

 the plot which had been deprived of potash, and the Bird's-foot 

 Trefoil was the most marked of the leguminous plants in the 

 same plot, because Clover and other taller leguminous plants 

 which usually keep out the Bird's-foot Trefoil had not grown 

 owing to the want of potash. Sorrel is found to be characteristic 

 of those meadows where nitrogenous manures, such as ammonium 



