WEEDS 



167 



Cocklebur, or clotbur. The different sorts of cockle- 

 bur are too well known to need description, but the 

 seedlings are not usually recognized. They are said to 

 be poisonous when eaten by stock. The burs fasten 

 themselves to animals, which scatter the seeds far and 

 wide. There are two seeds in each bur, and it is said 

 that one grows the first year but the other will not 

 germinate until the following year. Thus the plant 

 has a double chance to survive. 



Pigweeds. Figure 82 shows one of these in the early 

 stage, in which it is easily killed. Later on the root 

 gets very tough and woody, 

 and is hard to get out of 

 the soil. 



One of the pigweeds, 

 when dead and dry, is 

 loosened by the fall winds, 

 and goes rolling and tum- 

 bling over the ground, scat- 



FIG. 82. Young plant of pigweed. 

 (About natural size.) 



tering its seeds. On this 



account it is called "tumble 



weed. 7 ' There are a number of different "tumble 



weeds. " 



Knotgrass, or bird grass. This is a very common 

 weed all over the United States. It mostly lies flat 

 on the ground and yields a great abundance of black 

 seeds very much liked by canaries. These will sprout 

 even in very dry weather, so that the weed can spread 



