Weeds of South Africa. 



317 



popular articles without the use of many of these technical terms, 

 an illustrated glossary on the morphology of weeds has been prepared. 



Classification of Weeds. 



Weeds may conveniently be classified according to the time they 

 take, to complete their life-history, and three main types can be 

 recognized, namely cmvnal, biennial, and perennial weeds. 



Fig. 5. — "Canada Thistle" (^C'nicus n.rrensis), showing the underground 

 rhizome or root-stock. 



Annual Weeds are those in which the complete life-history is 

 completed within one growing season. The seed germinates and the, 

 resulting plant produces roots, stem, leaves, flowers, fruits, and seeds 

 all in the same season, and then dies. The Mexican Poppy {Argenione 

 Mexicana), the Mexican Marigold {Tagetes viinuta), the Khaki Weed 

 (Alternanthera achyrantha), Cocklebur (Xanthium occidentale), 

 Burweed (Xanthium spinosum), are examples of this type. 



Biennial Weeds complete their life-history in two growing 

 seasons. Germination takes place in the spring and during the first 

 season only root, stem, and leaves are formed. The leaves often 

 consist of a rosette pressed closed to the ground. In the second season 



