Direct relation between growth and frost hardening in cabbage leaves.

Potted cabbage plants were grown in growth chambers at 25 degrees day and 15 degrees night and hardened successively at 5, 0, and -3 degrees . Leaf growth was determined by measuring leaf area, hardiness by freezing at a series of temperatures and determining percent survival. Leaf growth increased progessively with leaf number, reaching a maximum rate of growth and final area in the tenth and eleventh leaves when the plants become potbound. Leaf growth continued at hardening temperatures of 5 or 0 degrees , the Q(10) being 2.0 to 2.5. Ability to harden also increased with leaf number, paralleling the growth rate of the leaves just before hardening as well as the growth rate and the total growth during hardening. The above results were similar whether prolonged (several weeks) or brief (24 hr) hardening was utilized.