Fig. 5. (A) Longitudinal section stained with Safranin, Fast Green, and Orange G, of a cold-hardened oat crown frozen at –13°C and then allowed to recover for 3 wk at 13°C in planting medium. This section is from the plant in Fig. 1E that was rated as a nonsurvivor. Note that the whole plant appeared dead (Fig. 1E) but at 3 wk a seemingly new shoot had emerged. Note the dark staining region that forms what looks like a barrier between disintegrated tissue and normal tissue. (B) Abnormal phloem from leaf-base tissue. (C) Abnormal phloem from the leaf base of a tiller that had not been damaged as badly as the leaf base from the opposing tiller. (D) A vascular bundle in cross-section showing what appear to be plugged vessels as compared with controls in Fig. 2C and 2D. (E) Interior portion of the crown core showing disintegrated cells with little evidence of structure. Inset: A closer view of the putative barrier from a different section of the same plant. Note the abnormal nuclei in the parenchyma cells outside the barrier. In this instance the barrier clearly did not prevent the occurrence of nuclear damage. The unlabeled bar in each subpanel is 100 µm.