Distribution and Propagation. 47 



then given opportunity to produce plants 

 in centers perhaps hundreds or thousands 

 of miles distant from the nearest point 

 where any of the same species may be 

 growing. In this fact we find an explana- 

 tion of the sudden appearance of weeds in 

 new centers where their presence otherwise 

 would be hard to account for ; and this is 

 more especially true of sections in proxim- 

 ity to cities. 



As a similar method of weed distribu- 

 tion, it may be mentioned that in the days 

 of early settlement, travelers used to carry 

 many weed seeds in the provender that they 

 brought with them for their horses, and 

 which the animals ate by the road sides, or 

 wherever convenient ; and the same state- 

 ment is true of the pioneer settlers of the 

 Northwest, who thus often introduced 

 weed seeds into their allotments before they 

 sowed their first crop. 



6. Road and farm vehicles. Noxious 

 weed seeds are frequently brought to farms 

 by the wheels of vehicles which have been 

 driven 'along the highway. The spread of 

 ragweed furnishes a familiar example of 

 this sort of weed distribution. The seeds 

 of this weed, and also of others that grow 



