Citric-acid Induced Loss of Rigidity in Potato Tuber Slices

and petiole, the interveinal tissue did not reach tritium equality with major veins, the stem, or the external solution. Water of the interveinal tissue maintained a stable tritium content at 60 to 70 % of external concentration for long periods. The pattern of results obtained was similar in sunflower and tobacco. Tritium content of leaf-tissue water vapor transpired by the canopy of an intact sunflower plant raised from seed in THO and treated with a stream of dry air inside a closed chamber increased over a 12-hour period. At the end of this period, interveinal tissue water and transpired vapor reached at least 95 % of the external tritium concentration about the roots. It was shown that the lack of equilibration in interveinal tissue should be attributed to exchange of tritium between the leaf and the surrounding unlabeled water vapor of the atmosphere. The results reported here contradict the hypothetical concept that a sizable fraction of tissue water is inaccessible for turnover.