Fig. 1. Freezing tolerance of three annual bluegrass ecotypes acclimated to the following conditions: nonhardened (NH); hardened 2 wk at 2°C (H2); hardened 2 wk at 2°C followed by 2 wk at -2°C (HF); hardened 4 wk at 2°C (H4). Freezing tolerance is expressed as 50% killing temperature (LT₅₀)

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