THE FROST-HARDENING MECHANISM OF PLANT CELLS

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Abstract
As compared with unhardened cells, hardened cells resist injury by deplasmolysis better, and round up more rapidly in plasmolysis (Catalpa, cabbage, etc.). but the relative volume of protoplasm and vacuole changes but little if at all (apple cortex, onion) in hardening, and resistance to acid and to heat does not change (cabbage). During hardening the osmotic pressure is increased, especially in the hardier woody plants (many woody and herbaceous spp.); non-solvent space ( = colloids and bound water). if present in measurable amount, increases markedly (Catalpa and Liriodendron), but the increase is greater in the vacuole than in the protoplasm (Catalpa) (non-solvent space is practically absent in cabbage, hardened as well as unhardened); and permeability to polar compounds increases, the more the increase the hardier the plant (many woody and herbaceous species). The press juice of hardened cabbage plants shows: precipitation of colloids over a wider zone in the pH scale; a slightly higher pH; and an unchanged buffering capacity. Artificial change in the pH of the sap in life does not affect hardiness (cabbage). The most pronounced and unmistakable changes in the protoplasm are increased permeability and lowered viscosity; in the vacuole, increased osmotic pressure and (in trees) non-solvent space. Ways are suggested in which all of these protect the cells against mechanical injury due to frost.