48 PVeeds. 



along the public roads, are carried in the 

 mud and dirt and dust that cling to the 

 wheels of every passing vehicle, and in 

 this way they are brought onto the farm. 

 Sometimes they are thus conveyed for 

 miles, not merely by the vehicles used by 

 the farmer himself, but also by those 

 belonging to others; from this sort of inva- 

 sion the farmer is, in a sense, powerless to 

 protect, himself. In a similar manner, weed 

 seeds are also conveyed from one part of 

 the farm to another. 



/. Implements of tillage. Weeds are, to 

 a considerable extent, distributed by the 

 ordinary implements of farm tillage, to 

 which they cling during the various pro- 

 cesses of cultivation. While this is true to 

 some extent of all kinds of weeds, it is 

 more especially true of those weeds which 

 multiply by means of creeping root-stocks. 

 These root-stocks readily cling to the plow, 

 harrow, or cultivator, and are thus carried 

 from one portion of a field to another, or 

 even from one field to another; and thus 

 new centers of distribution are constantly 

 being established. This is especially true 

 when the ground is so damp that it tends 

 to stick to the imulements used. Seeds or 



