The External Features of Stems 



125 



Fig. 71. Plantation of Norway spruce, showing whorls of branches at base of each year's 



growth. 



Determining annual growth of shoots from terminal-bud scars. 



Since the terminal bud marks the end of each year's growth, 

 the terminal-bud scars mark off a perennial stem into segments, 

 each of which represents the growth of a single year (Fig. 65). 

 Often an interesting life history is suggested by the varying 

 length of the intervals between the bud scars on a particular 

 stem. By a study of these intervals we can determine the 

 seasons that were favorable and those that were unfavorable 

 because of drought, excessive rain, attacks of insects, or some 

 other cause. 



In the pines and spruces the year's growth is marked off not 

 only by the bud scars, but also by whorls of branches. Dif- 

 ferences in the color of the bark and in its texture will also help 

 to distinguish successive annual stem segment in most trees. 



