. Carnegie Institution of Washington publication. . THE CORRECTION AND COMPARISON OF CURVES OF GROWTH. 127 Evidently a "correction for longevity" is as necessary as one for age. It is applied in the same way. Figure 27 illustrates the method. The horizontal line in this case indicates groups of trees of a given species. Group (A) on the right con- sists of trees 500 years old, group (B) of those 400 years old, (C) 300, and so forth. The vertical coordi- nates represent the amount of growth made by the ^ â, t i i ,-. â â . ,â r^ 1 . ,, r- , 1 1 T, -11 1 ,1 , ,1 Fig. 27.âIdeal Curve il
. Carnegie Institution of Washington publication. . THE CORRECTION AND COMPARISON OF CURVES OF GROWTH. 127 Evidently a "correction for longevity" is as necessary as one for age. It is applied in the same way. Figure 27 illustrates the method. The horizontal line in this case indicates groups of trees of a given species. Group (A) on the right con- sists of trees 500 years old, group (B) of those 400 years old, (C) 300, and so forth. The vertical coordi- nates represent the amount of growth made by the ^ â, t i i ,-. â â . ,â r^ 1 . ,, r- , 1 1 T, -11 1 ,1 , ,1 Fig. 27.âIdeal Curve illustrating Correction trees durmg the nrst decade. It will be seen that the ^^j. Longevity. trees 100 years old made an average growth of 2 inches; those 200 years old, inches; 300 years old, inches; 400 years old, inches; and 500 years old, inches. From this it appears that if the minor fluctuations of climate which took place from year to year during the first decade of the average tree 500 years old are to be compared with those during the corresponding decade of the average tree 200 years old, the growth of theolder trees must be multiplied by -i- = , the corrective factor for longevity. The process is clearly the same as that of obtaining the corrective factor for ageâthat is, it consists in multiplying the value of each point of a smoothed ideal curve by a corrective factor which reduces the curve to a straight, horizontal line. The determination of the corrective factor for longevity, however, is more difficult than the determination of that for age, not because the factor for longevity is any less real or is any less strictly a mathe- matical function, but because more trees are required in order to secure accuracy. Wliere the number of trees amounts to 200 and the age does not exceed more than 300 or 400 years the factor can be determined with a considerable degree of accuracy. For older trees a larger number of specimens is nece
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