CHAPTER XXVII 

 WEEDS 



684. Definition. A weed is any plant which is growing 

 where it is not wanted; i. e., a plant out of place. A stalk 

 of corn in an oat field is just as much a weed as is a thistle, 

 though it may do less damage and in its place be a very use- 

 ful plant. A plant may thus be a weed under some condi- 

 tions, while it is not under others. Many of the wild plants 

 of our native meadows and pastures must now be classed as 

 weeds, though before the land was put to use by farmers 

 they could hardly have been so considered. The smaller 

 plants in a forest are not weeds, for they are of use in shad- 

 ing the ground, preventing washing, and protecting the young 

 tree seedlings. 



685. Need for a Study of Weeds. A study of weeds is a 

 very useful and necessary part of a study of field crops. 

 In the production of every crop weeds must be considered, 

 and it is well to know their habits and how best to keep them 

 in check. A method of treatment that is efficient in destroy- 

 ing one weed or class of weeds may furnish a means for the 

 spread of some other, and it is therefore necessary to be able 

 to recognize the principal weed pests and to know how to deal 

 with them. The seeds of some of the most troublesome 

 weeds frequently occur in grain or grass seed, hence it is 

 important to be able to recognize them and to avoid sowing 

 them with useful crops. 



CLASSES OF WEEDS 



686. Basis of Classification. Weeds are classified accord- 

 ing to the length of time they live, as annuals, biennials, 



