Respiratory activity of mitochondria isolated from fresh and aged potato tuber tissue has been determined. No significant change in activity of the particles (expressed per unit N) was observed as a result of aging. However, the yield of mitochondrial material increased with aging. It has been suggested that the commonly observed stimulation of respiration that accompanies aging of potato tissue can be attributed largely to an inerease in the mitochondrial population rather than to a stimulation of the particles per se, and that this increase results from a fission of pre‐existing mitochondria. The respiratory activity of mitochondria isolated from unaged tissue was found to decline following storage of the tubers in the cold for extended periods. This decline was attributed to a loss of cristae structure in the particles, as observed microscopically. The possibility that this reduction in structural organization might be associated with changes in the state of dormancy of the tissue was considered.

Disks of potato tissue were aged by two separate methods. The resulting enhaiicetl respirations differed both qualitatively and quantitativety. It is suggested that the diverse results previously reported indicating changes in the terminal oxidative steps and/or in the relative contributions by competing metabolic pathways to the total respiration reflect variations in the methods employed to age the tissues. The nature of the stimulated respiration is discussed in terms of removal or retention of metabolites within the tissue during aging.

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