AGE CYCLE IN PLANTS AND LOWER ANIMALS 261 



such cases a certain degree of senescence is followed automatically 

 by reproduction and rejuvenescence. The agamic reproductions of 

 advanced age are often more highly specialized in character than 

 those of earlier periods of the life history. 



Senescence may be retarded or compensated in many forms by 

 conditions which induce frequent agamic reproduction, while under 

 other conditions senescence may be accelerated and death may 

 occur. The relation between senescence and rejuvenescence de- 

 termines whether an organism undergoes progressive senescence 

 and passes through a definite life history or persists indefinitely in a 

 certain physiological condition, apparently without a definite life 

 cycle. 



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