FARM CROPS. 199 



the sunlight necessary for their development. 4. A 

 few plants, as the dodders for instance, are parasites, 

 and derive their nourishment directly from the juices 

 of the plants on which they grow. 



Eradication of Weeds. The chief interest a farmer 

 has in weeds is to get rid of them. This is accom- 

 plished in various ways. Thorough cultivation which 

 prevents the development of leaves will in time kill any 

 weed. Plants, such as Johnson grass and Canadian 

 thistle, which have a reserve supply of food stored in 

 their roots, will take much longer to kill by this pro- 

 cess than others lacking this advantage. No new ma- 

 terial can be produced, however, without the aid of 

 chlorophyll, the green substance of plants, so sooner 

 or later the plants must die if the leaves are not al- 

 lowed to grow. This same result is accomplished on 

 small patches of bad weeds by covering them over with 

 straw, boards, or pieces of building paper held in place 

 by a few shovelfuls of dirt. 



Chemicals as Weed Destroyers. In the last four 

 or five years much attention has been paid to the use 

 of chemicals as weed destroyers. Spraying wheat- 

 fields infested with wild mustard with a 20 per cent, 

 solution of sulphate of iron has been successful in de- 

 stroying the mustard without injury to the wheat. 

 Heavy applications of common table salt will kill all 

 kinds of weeds, but unfortunately it makes no distinc- 

 tion between weeds and other plants in this respect. 



Proper Cultivation Keeps Down Weeds. Improv- 

 ing the fertility of land tends to lessen the trouble with 

 weeds. On rich soils the cultivated crops are able to 

 make sufficient growth to keep the weeds in check 

 the reverse happens on soils lacking plant food. Usu- 

 ally the poorer a farm is in fertility the more liberally 

 is it stocked with weeds. 



Preventive Measures. Preventive measures will do 

 much to keep a farm from getting infested with weeds. 

 All weeds along fences and other uncultivated places 

 should be cut before they form seed. These waste 



