Senile Changes in Leaves of Certain Plants 365 



Rejuvenescence is the process of restoring the original arrangement 

 in the colloidal units of the protoplasmic colloids. Sexual reproduction 

 is one method by which this is accomphshed, while in sexless plants more 

 primitive methods are used. 



Whether the progress of senility in sexual plants and animals can be 

 stopped, or even retarded, by such means of rejuvenescence as are utilized 

 in sexless forms, and thus to a certain degree are applicable to somatic 

 cells generally, is a problem for the future to solve. The present knowledge 

 of the cause of senile degeneration does not justify an unqualified denial 

 of the possibiUty of somatic rejuvenescence. 



ACKNOWLEDGMENTS 



The writer takes pleasure in expressing his indebtedness to Dr. Lewis 

 Knudson, of Cornell University, and to Dr. B. M. Duggar, of the Missouri 

 Botanical Garden, for many valuable suggestions in the preparation of 

 this paper. He also acknowledges the leave of absence granted to him 

 by his own institution, the University of Cincinnati, which enabled him 

 to hasten the completion of this stage of the .work. 



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1870 Ueber den einfluss des wachsthumsmediums auf die gestalt der 

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1875 Degeneration aus alterschwache. Monatschr. beforderung des 

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1902 Klima und blatt bei der gattung Quercus. Flora 90: 114-160. 



Buch, C. L. von 



1852 Uber blattnerven und die gesetze ihrer vertheilung. Ber. Konigl. 

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Burgerstein, A. 



1895 Ueber lebensdauer und lebensfahigheit der pflanzen, Wiener 

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