46 



STEMS 



inches in height, but are ranked as shrubs because their woody 

 stems do not die to the ground in winter. 



Herbs are plants whose stems above ground die every winter. 



60. Annual, biennial, 

 and perennial plants. 

 Annual plants are those 

 which live but one year, 

 biennials those which 

 live two years or nearly so. 



Some winter annuals 

 do not flower until 

 their second summer. 

 This is true of the even- 

 ing primrose and the 

 fringed gentian, and of winter wheat and rye 

 among cultivated plants. 



Perennial plants live for a series of years. Many kinds of 

 trees last for centuries. The California giant redwoods, or 

 Sequoias (Fig. 33), which reach a height of over 300 feet under 



FIG. 37. A portion of a 

 branch of Fig. 36 



Natural size 



FIG. 38. Twigs and 



branches of the 



birch 



favorable circumstances, live nearly 2000 years; and some 

 enormous cypress trees found in Mexico were thought by Pro- 

 fessor Asa Gray to be from 4000 to 5000 years old. 



