Reproduction in Relation to Agriculture 231 



ficult. By changing the crop from year to year so as to fol- 

 low or precede the crop of small grain with a crop like corn, 

 that is cultivated at intervals during its development, the 

 weeds may to some extent be held in check. Grazing animals, 

 particularly sheep, may aid greatly in removing weeds from 

 pastures. 



In grainfields, pasture lands, and meadows some success in 

 weed control has recently been attamed by the use of solu- 

 tions of poisons, particularly copper sulfate and iron sulfate. 

 The fields are sprayed with the poisonous solution while the 

 plants are young. Grasses are not greatly injured by the 

 spray and recover quickly, while weeds Uke the dandeUon, 

 wild mustard, and corn cockle are killed. 



In order to control the weeds in sugar-cane fields, some fields 

 are now covered with paper. The strong, spearlike shoots of 

 the sugar cane break through the paper, but the weed seed- 

 lings do not. The paper is made from the pulp left aft^r the 

 sap has been pressed out from the cane. Formerly this pulp 

 was wasted, but now it has been put to good use in the form of 

 field paper. 



Weeds should not be allowed to ripen seeds. The state 

 laws which require that weeds be cut along the roads aim not 

 so much at the removal of the unsightly plants from the 

 roadsides as at the protection of farmers from the seeds. 



Seed that is to be planted on any farm should be examined 

 for weed seeds. If they are present, the seed should be either 

 cleaned or rejected. Many a farmer plants his weeds with liis 

 grain. 



