THE STEM AND THE LEAF 



61 



per year continues to increase, and then diminishes. For ex- 

 ample, the long-leaf pine (fig. 229) grows only about | inch 

 the first year. For the first fifty years it makes an average 

 annual growth of 14 or 15 inches ; for the next fifty years, 4 or 

 5 inches ; and from one hundred years to extreme old age, 

 about 1|- inches. It usually lives about two hundred years. 



FIG. 41. An isolated white oak tree destroyed by a violent windstorm 

 Photograph by Paul Sargent 



The growth of the younger portions of most plants is quite 

 unequal, as may be learned from the study of a rapidly growing 

 stem, such as the morning-glory. 1 It will also prove interesting 

 to measure such plants as corn, broom corn, hemp, and pole 

 beans, to determine whether they elongate more by day or 

 by night, and during warm or during cool weather. 



1 For an illustration of this unequal growth, see Bergen and Davis, 

 Principles of Botany, p. 17. Ginn and Company, Boston. 



