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The reaction anatomy of 15 primitive dicotyledonous species is described. In 10 species there are differences between the wood from the upper side and lower side of inclined branches. These differences are (i) in the lignification of the secondary cell wall of fibres, (ii) in the number and diameter of vessels, and (iii) in the size of rays. In addition, tension wood fibres occur in three species.
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Kučera et al. (1977) studied this question.
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