On the causes of spiral grain in corewood of Radiata pine

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Abstract
Spiral grain in radiata pine (Pinus radiata D. Don) is mainly a defect of corewood and is seldom strongly developed in wood occurring more than 10 growth layers from the pith. Development of spirality in this species can be explained in terms of spiral flow of metabolites induced by the phyllotaxy of the vascular supplies to short shoots (the “needle traces”). Experiments are described in which spiral girdling and similar techniques are used to change the orientation of newly formed xylem elements so that they are in alignment with the altered direction in which metabolites and growth substances flow. By these means grain angles as large as 45° to the stem axis have been produced within one season's growth. Lesser but highly significant changes of grain angle have been brought about by modifying the dimensions and phyllotactic patterns of needle traces. The experimental trees have provided outstanding material for studying the anatomical bases of these changes which indicate an extremely plastic reorientation of the cambial cells.

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