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The free amino acids proline and glutamic acid increased in the crown of winter wheat in all treatments when exposed to coldhardening. Glutamine also increased except when 90-80 N-P fertilizer was applied. The increase of proline and glutamic acid was enhanced with the application of P but counteracted by N. This enhancement was smaller with glutamine. The decrease of threonine, tyrosine, phenylalanine, lysine and tf-aminobutyric acid with cold-hardening was not counteracted by application of N and P.However, isoleucine in cold-hardened winter wheat increased with the application of 180-0 fertilizer and aspartic acid increased when P was added. The increase in alanine with cold-hardening was enhanced 1104 KALDY AND FREYMAN by P alone but counteracted by N-P treatments. The marked increase in proline during cold-hardening could be useful in the detection of cold-hardiness in winter wheats.

Ice sheets frequently result in widespread damage to herbaceous plants in temperate latitudes; the cause of injury is a matter of controversy. In a series of experiments with alfalfa in which artificial ice sheets were formed over essentially unfrozen soil, marked changes in the soil atmosphere were recorded. Under one ice sheet, for example, which lasted for 50 days, soil CO2 rose to 8.7% and alfalfa plants died. From observations such as this and from experiments in which the CO2, O2, and N2 in ice‐covered soils were artificially altered, it was concluded that CO2 accumulation is the prime factor in the death of herbaceous plants under ice sheets. Intermittent thawing of artificial ice sheets reduced or eliminated injury. Stubble protruding through the ice sheet did not prevent injury.

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