176 FRIENDS AND ENEMIES OF PLANTS 



onions and ragweeds when eaten by cows taint their milk and 

 make it undesirable for use. 



8. Weeds generally afford a natural harbor for dangerous 

 reptiles and injurious insects, which have their breeding grounds 

 in such places. 



9. Weeds shade our fences and hasten their decay. 



10. Weeds suggest carelessness and neglect. 



Are Weeds ever Beneficial? If your instructor should ask you 

 whether weeds were ever beneficial, perhaps you would not hesi- 



Russian thistle. Quack grass. 



tate to say no, but your answer would not be strictly correct. 

 Sometimes farmers find it of some advantage to let a field rest 

 and grow up in weeds under certain conditions. Before the 

 weeds mature or get too large they are plowed under and thus 

 form a rich manure for the soil. The weeds also shade the ground 

 and prevent it from baking. 



Kinds of Weeds. There are three general classes of weeds: 

 (a) annuals, (b) biennials, (c) perennials. 



