WEEDS AND THEIR CONTROL 215 



seeds of the West. Information concerning the identifi- 

 cation of these may, however, be found in one or more of 

 the following bulletins: 



1. Farm Weeds Clark, Dominion Department of 



Agriculture, Ottawa. 



2. Better Farming -- Bulletin No. 31, Saskatchewan 



Department of Agriculture, Regina. 



3. Weeds of Alberta Alberta Department of Agri- 



culture, Edmonton. 



4. Plants Injurious to Stock Bulletin No. 7, Depart- 



ment of Agriculture, Ottawa. 



5. Weeds and Weed Seeds Bulletin No. S. 8, Do- 



minion Department of Agriculture, Ottawa. 



6. Weeds Used in Medicine Farmers' Bulletin No. 



188, U.S.D.A., Washington. 



7. Lessons on Weeds - - Bulletin No. 30, Manitoba 



Agricultural College, Winnipeg, Man. 



172. Duration of the Growth of Weeds. The duration 

 of growth of different classes of weeds varies consider- 

 ably, some completing their life cycle in one season, 

 .some in two or parts of two, while others live three 

 years or more. Thus we have annual, biennial, winter 

 annual, and perennial weeds, each type requiring a dif- 

 ferent treatment for its control or eradication. An- 

 nuals die at the end of the first season's growth, winter 

 annuals start in the late summer or early fall and die 

 the next year, biennials die at the end of the second 

 year, while perennials may live an indefinite number of 

 years. 



Annuals, winter annuals and biennials can be com- 

 pletely controlled by preventing seed formation and the 

 introduction -of weed seeds to the farm, but to control 

 perennials not only must seed formation and the intro- 



