VEGETABLE PARASITES AND WEEDS 183 

 PLANTS AS AFFECTED BY WEEDS 



336. Weeds are plants of the higher orders that per- 

 sist in growing where they are not wanted. They in- 

 jure the desirable plants about which they grow by 

 robbing them of light, moisture and food, and their 

 presence is an evidence of slovenly culture. The re- 

 markable vigor and prolificacy possessed by many weeds 

 would enable them to soon overcome most cultivated 

 plants, but for the aid of the cultivator. As with harm- 



FIG. 83. Propagation: showing how plants of the sow thistle multi- 

 ply from underground stems. 



ful insects and fungi, prompt and persistent efforts are 

 essential to the control of weeds in most cultivated grounds. 

 337. Kinds of weeds. With reference to their term 

 of life, weeds and other plants are divisible into three 

 classes, viz. : annual, those that live but one season ; 

 biennial, those that live only two 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 commonly most tenacious of life and are there- 

 fore often most difficult to control. 



