Regeneration of re-covered bark in Eucommia ulmoides.

The girdled trunk of Eucommia ulmoides, sometimes could not regenerate a new bark due to ringed surface necrosis. But, if an extension of 10cm of the bark on each end of the necrotic part was removed in time and re-covered with new bark taken from another tree, the re-covered bark and the newly girdled part could heal together one week after. Opposite to the necrotic surface the loose part of the re-covered bark regenerated callus from the phloem ray cells. If the re-covered part was very close to the necrotic surface, no callus was regenerated. However, many scattered tracheid-like elements derived from phloem were found. And then groups of cells including several tracheid-like elements were discernible. There was a ring of meristematic cells around that group of cells. Finally these meristems gradually became normal and had usual activities of vascular cambium.