STEMS. 



43 



tected buds are formed on the twigs to their very tips. In 

 other shrubs — for example, in the sumach, the raspberry, 

 and blackberry — the shoots continue to grow until their 

 soft and partly matured tips are killed by the frost. 

 Such a mode of growth is called indefinite annual growth, 

 to distinguish it from the definite annual growth of most 

 trees. 



65. Trees, Shrubs, and Herbs. — Plants of the largest size, 

 with a main trunk of a woody structure, are called trees. 

 Shrubs differ from trees in 



their smaller size, and gen- 

 erally in their more forking 

 and divided stem. The 

 witch-hazel, the dogwoods, 

 and the alders, for instance, 

 are most of them classed 

 as shrubs for this reason, 

 though in height some of 

 them equal the smaller 

 trees. Some of the smallest 

 shrubby plants, like the 

 blueberry, the wintergreen, 

 and the trailing arbutus, 

 are only a few inches in 

 height, but are ranked as 



shrubs because their woody stems do not die quite to the 

 ground in winter. 



Herbs are plants whose stems above ground die every winter. 



66. Annual, Biennial, and Perennial Plants. — Annual 

 plants are those which live but one year, iiiennials those 

 which live two years or nearly so (see § 46). 



Some annual plants may be made to live over winter, 

 flowering in their second summer. This is true of winter 

 wheat and rye among cultivated plants. 



Fia. 27. — A White-Oak Tree, with Trunk 

 somewhat Deliquescent. 



