476 PRACTICAL BOTANY 



places. All fence rows, hedges, clumps of blackberry and 

 raspberry bushes, and similar lurking places for weeds, as well 

 as grassland and tilled ground, should be kept as clean and as 

 nearly weedless as possible. Weeds which have gone to seed 

 should not be plowed or spaded under, but allowed to dry 

 and then burned. It will be found well worth while to rake 

 away from fences and burn all such accumulations of tumble- 

 weeds as those shown in Fig. 356. Wild mustard, which is a 

 very troublesome weed in fields of the small grains, is read- 

 ily killed by spraying with a solution of copper sulphate or 

 iron sulphate. Weedy lawns are sometimes improved by very 

 careful salting, which does not injure the grass. Gravel walks 

 may be cleared of weeds by watering them with a solution of 

 sodium arsenate or of crude carbolic acid. 



