8 



WEEDS OF THE FARM AND GARDEN 



How Weeds Spread. Weeds are spread by means of 

 seeds, by vegetative reproduction, or by both seeds and 

 vegetative reproduction. 



Reproduction by Seeds. Most weeds reproduce them- 

 selves by seeds. One of the exceptions to this rule is the 



horse-radish, which 

 does not, so far as 

 we know, seed in 

 Iowa. 



It has been our 

 observation that the 

 Canada thistle usu- 

 ally does not seed in 

 Iowa, although spec- 

 imens of heads con- 

 taining seed have 

 been received from 

 different parts of 

 the state. It is also 

 probable that the 

 Canada thistle does 

 not seed so frequent- 

 ly in Iowa or in the 

 United States as in 

 Europe. 



Vegetative Repro- 

 duction. Many 

 weeds multiply by 



means of roots, 



Fig. 2. Woolly thistle, a type of perennial _ tp nr u ni .u r n 



root. as l 



quack grass, one 



means of multiplication is by stems commonly called 

 "roots," which are divided into a series of joints at which 

 new shoots are produced. The same structure occurs in 

 germander or wood sage. Horse-radish may be propa- 

 gated by roots exclusively. In another type, like the 



