The Metabolism of Senescent Leaves 209 



Conclusions 



With regard to respiratory activities and the metabolism 

 of proteins in ageing leaves the following conclusions may be 

 drawn from the data : 



1. The predominance of catabolic changes in the tissues 

 results, in part, from a decline in synthetic activity, and not 

 solely from an increase in hydrolytic breakdown of complex 

 constituents. 



2. High rates of respiration are generally found in yellow- 

 ing leaves; much of the carbon dioxide may arise from the 

 oxidation of the carbon skeletons of amino acids. 



3. It is possible that both the high rate of respiration and 

 the loss of synthetic activity result from changes in the phos- 

 phorylating mechanisms of the cells. 



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