EXPERIMENTS ON LONGEVITY 



403 



death is fundamentally and inherently con- 

 tinuous from the time that breakdown 

 starts until the last cell is dead. 



We have studied various "end-points," 

 and have found the most reliable and 

 least variable, because capable of being 

 read with the greatest certainty, to be the 

 beginning of death, as evidenced by the 

 first appearance of abnormality of the 

 stem, in the continuous series which in- 



period and the period of suspended anima- 

 tion, and therefore by necessary conse- 

 quence the total duration of life, varies 

 considerably from individual to indi- 

 vidual. Now if we determine the cor- 

 relation between the rate of growth during 

 the growing period (that is, the increase 

 in stem length of the seedling per unit of 

 time), on the one hand; and the total 

 duration of life to the beginning of death, 









































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Days of Growth 



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Fig. 9. Observed (Circles) and Calculated (Smooth Curve) Mean Stem Length of Canteloup Seedlings 

 Grown in the Complete Absence of Exogenous Food and Light 



variably ends finally in the complete death 

 of the seedling. 



In such an experiment the seedling 

 grows in length in close correspondence to 

 a logistic or autocatalytic curve. This 

 curve has been found widely useful in 

 describing the course of growth in both 

 individuals and populations. How closely 

 the actual experimental results with the 

 canteloupe seedlings, under conditions 

 of inherent vitality, follow the logistic 

 curve, is shown graphically in figure 9. 



The time duration of both the growth 



on the other hand, the correlation comes 

 out to about —0.5 or —0.6. This is a 

 substantial correlation. It demonstrates 

 that there is a significant association 

 between individual differences in rate of 

 growth on the one hand and duration of 

 life on the other hand, in this group of 

 seedlings, grown under such conditions 

 that both of these phenomena are neces- 

 sarily dependent solely upon the inherent 

 vitality of the individual as here defined. 

 There can be no reasonable doubt as to 

 the correctness of the conclusion that con- 



