EFFECT OF SEVERAL ENVIRONMENTAL FACTORS ON THE HARDENING OF PLANTS

Abstract

Plants of wheat, alfalfa, cabbage, and tomato were subjected to several combinations of environmental conditions before and during hardening treatment. Except with tomato, warm days with cold nights during hardening were somewhat less efficient than continuous cold in inducing the development of the hardened condition; cold days and warm nights were ineffective in causing hardiness. No combination of light and temp. was effective in causing hardening in vegeta-tively active plants (low in organic reserves) if CO2 for photosynthesis was withheld during hardening. Actively growing plants hardened very little if at all when stored at low temp, in the dark. Long days and short nights, at a continuously low temp., were more effective in causing hardening than the reverse. To the contrary, a long warm day, with a cold night, usually was highly detrimental to the hardening process, in wheat and alfalfa, especially in plants previously grown with a short day. Any conditions which would seem to favor photosynthesis and lessen respiration and growth assisted the hardening process.