348 



CONTROL OF WEEDS 



bulbs that will grow in any position are also difficult to get rid of 

 by a limited amount of tillage. Thorough and frequent cultivation 

 however, will destroy weeds of this type. 



Weed Dissemination. — All three classes of weeds bear seeds and 

 are spread by this method for long distances. Weeds that form 

 their seeds in burs, such as burdock, cockle bur, sand bur, bidens, 

 Spanish needles and others are often carried on the coats of animals 

 for long distances. They literally catch rides to their new homes. 



Tickle grass, tumble weed, 

 and a few others of that type F 10 - 2i5 - 



spread by the whole body car- 

 rying seeds, rolling in the wind 

 for miles and miles. Occasionally 

 these are carried high in the air, 

 but usually are found rolling on 

 the ground. Many seeds, such as 



Fig. 244. — Purslane; entire plant. (Minnesota Station.) 

 Fig. 245. — Buckhorn Plantain; 1, entire plant; 3, seedling; 4, seed enlarged. 



Station.) 



(Minnesota 



milkweed, dandelion, thistle and others may be carried by strong 

 wind to distant places. Still others, such as the dock and wild 

 carrot, may be blown somewhat by the wind and will also 

 float upon water, where they are carried by either waves or cur- 

 rents to new fields. 



Many perennial weeds have other means of spreading than by 

 seeds. The underground stems, runners, etc., will spread weeds. 

 Some of the worst grasses, Canada thistle, sheep sorrel, toad flax 

 and many more are thus spread. Frequently such seeds are 



