THE RELATION OF CABBAGE HARDINESS TO BOUND WATER, UNFROZEN WATER, AND CELL CONTRACTION WHEN FROZEN

Abstract

Calori-metric detns. were made on hardened plants at [long dash] 5.6[degree]C, on unhardened ones at [long dash]5.6[degree] and [long dash]2.1[degree]C. The hardened plants suffered 50% killing at the former, the unhardened 85% killing at the latter temp. A knowledge of the total moisture and the freezing point allowed a separate calculation of osmotically and non-osmotically bound water on the assumptions that the latter does not act as a solvent, and that the plant sap is an ideal soln. The results oppose the dehydration theory of frost injury, for the unhardened plants contained more total unfrozen water and more non-osmotically bound water at [long dash]2.1[degree]C than did the hardened at [long dash]5.6[degree]C. Less ice was formed per g. fresh wt. in the unhardened than in the hardened. This opposes the pressure theory. In agreement with the theory of protoplasmic strain, the cells of hardened plants were contracted to 1/3. those of unhardened to only 1/2 of their normal volume at the above temps., indicating a greater resistance to strain in the hardened state. Rate of freezing and thawing did not alter the injury to unhardened plants. Slow freezing reduced the injury to hardened plants, but slow thawing did not. These facts favor the assumption that extracellular ice occurred in the unhardened in all cases. In the hardened plants intra-cellular freezing may have occurred when freezing (at the lower temp.) was rapid, and the cells may have been capable of surviving an even more severe contraction under conditions of slow freezing than mentioned above.