THE SAPWOOD-HEARTWOOD TRANSITION

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Abstract
The transition from sapwood to heartwood in certain species has been described in detail, and the formation of intermediate wood discussed. The distinction between sapwood and heartwood cannot always be clearly made on the basis of colour, or on the presence of starch or tyloses, but must be based on the fundamental change which lies behind these other features—the death of the cells of the vertical parenchyma and the rays. Some Australian timbers have a sharply defined heartwood, others have no heartwood, others have a band of intermediate wood, which is sapwood, but approaches heartwood in some features. The formation and characteristics of this intermediate wood is described for three species, Nothofagus cunninghamii Oerst, Sloanea woollsii F. Muell., and Diospyros pentamera F. Muell. An explanation is offered of the paradox that the death of sapwood cells in the living tree causes changes that result in the formation of heartwood, but that these changes do not take place with the death of the sapwood cells on felling or when the whole tree dies.

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