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, lke the 
blueberry, the wintergreen, 
and the trailing arbutus, Fig. 27. — A White-Oak Tree, with Trunk 
are only a few inches in somewhat Deliquescent. 
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, biennials 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. 
