the annual. The seed germinates in the fall, a mat of leaves is 

 produced and the next spring a stalk is sent up which produces 

 flowers and seed, then dies. Shepherd's purse, wild barley or 

 squirrel tail, pepper grass in our climate, but in the south 

 many more weeds belong to this class. Winter wheat and win- 

 ter rye are winter annuals. 



Biennial. The seeds of biennial weeds germinate in the spring, 

 the plant produces a mat of leaves with a short stem, it passes 

 through the winter in this way, the next season it sends up a 

 stem on which flowers and seed are produced. This ends its 

 existence. Burdock, Parsnip, Carrot, Mullein, and Bull Thistle 

 are representatives of this type. These weeds are common every- 

 where in the ?tate. 



Perennial. Ti^ nerennial weeds are often long lived. The 

 seed germinates, somtL'mes a stalk with flowers is produced the 

 same season. The ^lant continues to live year after year. Peren- 

 nial weeds are thv most difficult to exterminate. Weeds of this 

 type are numerous and in Iowa are represented by Canada 

 thistle, Morning glory, Milkweed, Quack grass, Nimble will. 



HOW WEEDS SPREAD. 



Weeds spread in two days by (1) vegetative propagation and 

 (2) seed production. Some weeds have both methods, some 

 only one. 



Vegetative Propagation. In this method of reproduction the 

 stem or root serves to propagate the plant. This is brought 

 about in three ways, (a) by stem above ground or under- 



Tumbleweed (Amaranthus graecizans) . Scattered by the wind against 

 fence. ( Bergen. ) 



