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PHYSIOLOGICAL ASPECTS OF AGING 



IN PLANTS 



William J. Rob bins 



I intend to limit my discussion to seed plants and to consider the aging of 

 seeds, individual plants, cells, and meristems. Well-authenticated information 

 on the physiology of aging in plants is scanty. We can safely say that cells, 

 organs, and individual plants age, but the physiological changes which occur 

 and the causes are ill defined and poorly understood. 



Even the definition of age differs. It may be measured from the last gametic 

 reproduction or from the establishment of an individual plant by any means, 

 either gametic or agametic. By the first method of measuring age, a cultivated 

 banana plant would be hundreds, if not thousands, of years old because there 

 is no record of the production of viable seed by the cultivated banana; it is 

 propagated entirely by vegetative means. By the second method its age would 

 be measured in days or months. 



Although age is usually expressed in units of time the concept of physiologi- 

 cal age, which depends on the condition of the plant rather than on the time 

 it has existed, has proved to be of some value. While I am prepared to admit 

 that a plant is as old as it feels, the difficulty is to determine how it feels. 

 Change in leaf shape has been used in some instances to estimate physiological 

 age. However, since for some plants leaf shape is markedly affected by the 

 external environment and is not determined primarily by the internal condi- 

 tion of the plant, this means of measuring physiological age is of limited 

 application. 



Seeds. The aging of seeds is a special problem within the province of this 

 topic because in this instance we have an embryo plant which lies dormant 

 for various periods of time but eventually loses its vitality if germination 

 fails to occur. 



The life span varies with the kind of seed and with the conditions of storage. 

 For example, the viability of embryos in the seeds of some kinds of willow 



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