242 



WEEDS 



would not be successful competitors or vagrants. Usually 

 they are (1) suited to a wide range of conditions', (2) strongly 

 tenacious of life; (3) have effective means of dissemination; 

 (4) and they often have a life-cycle similar to that of some 

 cultivated plant, and they therefore take the fortunes of that 

 plant. As examples of these categories, we may recall the 

 wide range of such plants as pigweeds (Fig. 408) and docks; 

 the tenacity and endurance of Canada thistles (Fig. 409) 

 and quack-grass (Fig. 27); the way in which the burdock 

 spreads its seeds; 

 the fact that cockle 

 (Fig. 181) ripens 

 with the wheat, and 

 the seeds pass 

 through the separa- 

 tor with the grain. 



409. Canada thistle. 



410. Wild carrot. 



411. Redroot pigweed. 

 Amarantus. 



412. Certain kinds of weeds follow certain crops or 

 certain systems of farming. Dandelion (Figs. 8, 302), wild 

 carrot (Figs. 194, 410) and whiteweed or daisy (Fig. 189) 

 are essentially weeds of grass lands; purslane, pigweed, 

 chickweed, redroot (Figs. 406, 407, 411), shepherd's purse, 

 are pests of gardens and tilled grounds; cockle, chess (Fig. 



