188 Principles of Plant Culture. 



seasons ; and perennial, those that live an indefinite 

 number of seasons. Weeds of the first class usually 

 seed most abundantly, and hence they are most widely 

 distributed and appear in cultivated grounds in the 

 greatest numbers. Those of the third class are com- 

 monly most tenaciotis of life and are therefore often 

 most difficult to control. 



338. Annual and biennial weeds, since they have a 

 definite life period and multiply almost exclusively by 

 seed, may be controlled by preventing seedage. To ac- 

 complish this with certainty, the plants should be de- 

 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- 



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

 underground stems. 



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

 den beneath the soil and are often extremely tenacious 

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

 eradicate. Parsistent prevention of leafage, by starv- 

 ing the protoplasm of the roots, is always effectual, 



