42 IVeeds. 



as freely as those of the useful clovers, 

 grasses, and grains; and owing, in very 

 many instances, to their similarity in size 

 to the useful seeds in which they are found 

 (especially in grass or clover seeds), it is 

 almost impossible, by any process of clean- 

 ing that may be adopted, to separate the 

 seeds of weeds from the useful seeds which 

 are intended for sowing. The distribution, 

 therefore, of these weed seeds is as wide as 

 that of the useful seeds in which they are 

 found, and, it may be added, is as continu- 

 ous. The seeds of millets are also a fruit- 

 ful agency for the dissemination of weed 

 seeds, though not perhaps to the same 

 extent as are seeds that are smaller. 



Renewing the stock of small grains by 

 the purchase of new seed, or by the 

 exchange for seed grown by others, is a 

 common practice among farmers, and it has 

 many things to commend it ; but along with 

 the new seed there too frequently comes an 

 influx of the seeds of the most troublesome 

 weeds. Although this is a less fruitful 

 source of weed-seed dissemination than that 

 which has just been spoken of, it furnishes 

 the explanation of the arrival upon our 

 farms of manv forms of weeds, the pres- 



