CLASSES OF WEEDS 523 



and perennials. It is desirable to know to which class any 

 weed belongs, because the methods of combating it depend 

 very largely on whether it lives one, two, or several years. 



687. Annuals. An annual is a plant which makes all its 

 growth in a single season. The seed germinates in the spring 

 or summer, the plant produces blossoms and seeds the same 

 year, and then dies. The seeds of some annuals germinate 

 in the fall and the plants live over winter, producing their 

 flowers and seed the following season, usually during the 

 spring and early summer months. These plants are known 

 as winter annuals. Corn is an example of an ordinary 

 annual, and spring wheat is another. Winter wheat, on the 

 other hand, is a winter annual. Bagweed, crabgrass, fox- 

 tail, and mayweed are annual weeds; shepherd's purse, corn 

 cockle, and cheat are usually winter annuals, though the seed 

 may not germinate till spring. Annuals spread only by 

 means of their seed. 



688. Biennials require two years to complete their 

 growth. The seeds germinate during the spring and summer 

 of the first year and the plants produce an extensive root sys- 

 tem, but do not develop much top growth. The following 

 spring they produce a large growth of top, blossom, ripen 

 their seed, and die. Like annuals, they spread only from 

 seed. The bull thistle and burdock are familiar examples of 

 biennials, as are also cabbage, turnips, beets, and a number 

 of other garden vegetables. 



689. Perennials. These are plants which may live an 

 indefinite number of years. This class includes all our trees 

 and shrubs, many ornamental plants, and such garden vege- 

 tables as rhubarb and asparagus. Many of our worst weeds 

 are perennials. Some perennials spread only from their 

 seeds ; others have running; rootstocks or underground stems 

 which grow from year to year and new plants may spring 



