CROPS AND WEEDS 127 



old pastures, is of this class. These weeds are sometimes 

 rather difficult to destroy the first season of their growth, 

 for they are apt to grow up again after being cut off. 

 If cut the second season, just before bloom, they soon die 

 without yielding seed. 



Perennials. Weeds of a third class continue to live 

 and bear seed from year to year, unless they are destroyed. 

 These are called perennial weeds. Some weeds of this 

 class, as the quack grass, sow thistle, and the wild morn- 

 ing glory, multiply from buds on underground parts as 

 well as by seeds. Perennial weeds are the hardest of all 

 to destroy. We learned in Lesson 4 that the food that 

 nourishes the roots of plants is formed in the leaves. If, 

 therefore, we prevent the leaves from growing, the roots 

 will soon starve. This is the surest way to kill perennial 

 weeds, although it is often hard to carry out. 



Constant Warfare. Most weeds spread chiefly from 

 their seeds, hence care should be taken to prevent the 

 formation of weed seeds. The more thorough we are in 

 keeping the weeds out of our land, the easier the work 

 becomes. While we may not hope to get rid of all weeds, 

 we may greatly lessen their numbers by keeping up con- 

 stant warfare against them. 



QUESTIONS AND EXERCISES. 



1. What are weeds? 



2. How do weeds injure a crop? 



3. Define annuals, biennials, perennials. 



4. How do each of these three groups of weeds spread? 



5. How can most weeds be kept from spreading? 



