Recovery of Turgor by Cut Shoots after Wilting.

When high tensions are developed in the water columns within the xylem of a shoot, the shoot wilts. If such wilting is induced by plugging a stem with gelatin immediately upon cutting, very rapid recovery results if the plugged portion is cut off under water in such a way as to prevent the entrance of air into the stem. Such recovery was observed by DIXON and BARLEE (1) as long as no gas entered the stem even if the basal portion was in a partial vacuum. Sometimes recovery under these conditions was not achieved instantaneously upon cutting the stem under water; but a brief release of air into the vacuum chamber in which the plant base was sealed caused recovery. Immediate recovery had probably been prevented in these cases by the creation of a gas phase causing a discontinuity between the water in the xylem elements and the external water. Water continuity was again established upon momentarily letting the cut portion come under atmospheric pressure. In order to enhance the keeping qualities of cut flowers, it is a common practice to pick them during a period in which the plant would be expected to have a favorable water balance. Often a searing or hot water treatment of the cut ends is employed to prevent plugging of the xylem by latex or phloem exudate. Cut shoots when wilted recover very slowly, if at all, when placed in water, but if the basal end of such a shoot is subjected to a strong hydrostatic pressure, water may be forced into the shoot overcoming the resistance in the stem and causing recovery (5). A similar experiment described by PFEFFER in 1897 is mentioned by RENNEIR (4). NEGER (3), while experimenting with a vacuum infiltration method of determining the degree of stomatal opening, found that wilted plants could be revived by placing them under water in a vacuum chamber. He suggested that perhaps horticulturists could find use for such a method. Recently HAMNER, CARLSON, and TUKEY (2) described a similar method of treating plant material. The whole plant or plant part was infiltered with water by means of the vacuum method. The water saturation thus attained improved the keeping qualities of certain succulent plants and cut flowers. Failure of moderately wilted shoots to recover immediately when placed in water usually is due to the presence of air in the xylem elements which restricts the passage of water. Any method which would effectively dispel the accumulated gas from the cut elements and reestablish the continuity between the external water and that within the conducting system of the plant should facilitate the recovery of the wilted shoot when it is placed in 152 PLANT PHYSIOLJOGY