WEEDS AND WEED CONTROL 



245 



Means of Distribution. When once introduced, weeds migrate in 

 a number of ways by natural and artificial means. The natural migra- 

 tion of weeds is favored by the possession of runners (slender radiating 

 branches), by elongating rootstocks, by running roots, by seed- throwing 

 apparatus, by having fleshy edible fruits with hard seeds, by flying seeds, 

 and winged fruits, by drifting over frozen ground, or snow, as tumble 

 weeds, (Fig. 100), by means of water-carried seeds, by attachment to the 

 hair and fur of animals by means of hooks and other devices. The artifi- 

 cial means are as follows: Roots, rootstocks and bulbs are sometimes 

 carried from field to field and from farm to farm by plows, harrows and 



PIG. 101. Extensive patch of bouncing bet (Saponaric officinalis) along an unused 

 railroad siding across Hackensack Meadow, July 15, 1916. 



cultivators. Seeds and other plant parts are carried away in the ball of 

 earth surrounding the roots of nurserystock. They are entangled in 

 packing material, in the waste from woolen mills, as the storksbill (Erod- 

 ium), in hay, in commercial seeds, which is one of the most frequent ways 

 of weed introduction. Weeds are carried along by the disturbance of the 

 air through the passage of trains (Fig. 101) and automobiles and on these 

 rapid means of conveyance. Weeds have been introduced as useful or 

 ornamental plants which have later escaped from cultivation. They 

 'have been introduced in ballast and along with the packing of commercial 

 articles. 



