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Diagram after Jaccard (1938). Diagrammatic representations of (a) Loop made in a conifer stem. Compression wood is hown as a thicker line on the lower sides of the upper and lower parts of the loop. (b) Loop made in a woody dicotyledon stem. Tension wood is shown as a thicker line on the upper sides of the upper and lower parts of the loop. (c) and (d) The effect of cutting the loops is similar in each case suggesting compression woodacts by pushing, while tension wood by pulling against the normal wood