Plants as Affected ~by Weeds. 187 



stroyed before bloom, as many species possess enough 

 reserve food to mature seeds sufficiently for germina- 

 tion, if cut while in flower. 



339. Perennial weeds often multiply by suckers as 

 well as by seeds (Fig. 80). Since the roots or under- 

 ground stems whence the suckers grow (114), are hid- 



FIG. 80. Showing how plants of the sow thistle multiply from 

 underground stems. 



den beneath the soil and are often extremely tenacious 

 of life, weeds of this class are frequently very hard to 

 eradicate. Persistent prevention of leafage, by starv- 

 ing the protoplasm of the roots, is always effectual, 

 though it is often very difficult to carry out, since the 

 suckers of some species grow with great rapidity. Yet, 

 on the whole, no better remedy is known. Frequent 

 plowing and cultivation of the infested ground is usu- 

 ally the most effectual means of preventing leafage. 



Certain very tenacious perennial weeds, as the Can- 

 ada thistle* and the sow thistle,f when growing on 

 deep, rich loams in which the roots spread freely below 

 the plow line, may, it is said, be crowded out by seed- 

 ing the land to grass, at less cost than they can be 

 subdued by the plow. 



* Onieus arvenns. f Sonchus arvnsis. 



