168 



A<;I;ONO.MY 



depend upon peculiar soil conditions may be eradicated by 

 changing these conditions. Sedges which delight in moist soil 

 may be exterminated by draining, and mosses, sorrel, and various 

 other plants that like acid soils may be driven out by liming 

 the soil. Perennial plants must either be starved out by fre- 

 quently cutting off the leaves, or they may be dug up. A 

 large number of weeds are also killed by spraying with iron 

 sulphate, or " copperas," in the proportion of six pounds of iron 



Photograph from Bergen and Caldwell's " Practical Botany" 



FIG. 117. A tumbleweed (Cycloloma) blown into heaps by the wind 



sulphate to four gallons of water. Grainfields may be practi- 

 cally freed from wild mustard in this way, the spray doing no 

 harm to the cultivated plants. All crops are not so resistant 

 and one must discover what the particular requirements of a 

 crop are before spraying. For destroying algse, the fine, fila- 

 mentous green growths that often appear in lily ponds and the 

 like, copper sulphate is often used. The water should be treated 

 with one part copper sulphate to three million parts of water. 

 Fish are very easily poisoned by this substance, and care must 



