WEEDS 



165 



toadflax, were originally brought from Europe as desirable 

 additions to the flower garden, and only later took up a free 

 life in the fields. A few of our weeds are native, but most of 

 our noxious species have been derived from the Old World, 

 where centuries of struggle with crop and cultivator have 

 developed to the utmost their ability to resist all attempts to 

 dislodge them. Nor are weeds entirely confined to specimens 

 growing in cultivated areas. The plants that come up in walks 



Photograph from American Steel and Wire Co. 



FIG. 114. Grainfield showing the effect of spraying with iron sulphate 

 The portion on the left is unsprayed. Note the abundant young mustard plants 



and drives, on railway embankments, and in similar places are 

 weeds. Other weeds, like the ditch moss and water hyacinth, 

 are confined to the water, but prove their weediness by chok- 

 ing up the streams and rivers, and in some cases actually 

 preventing navigation. 



Harmfulness of weeds. Weeds are harmful in several ways. 

 They absorb water needed for the growth of cultivated crops, 

 prevent the formation of plant food by shading, harbor fungous 

 and insect enemies, render more difficult the task of keeping 



