SEASONAL VARIATIONS IN THE SECONDARY PHLOEM OF SOME FOREST TREES FROM NIGERIA

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Abstract
Summary: Samples of bark were taken from the main trunk of trees of Antiaris (two), Tectona, Bombax, Albizia, Ricinodendron and Holarrhena at monthly intervals for two consecutive years. Phloem zones were characterized, inter alia, by the amount and type of callose present, as indicated by the callose fluorescence. The greatest amount of the ‘active’ phloem coincided in all cases with some part of the rainy season. Bud break generally occurred at some time during the dry season, normally at the very end, and this coincided with the lowest amount of ‘active’ phloem, although it was rapidly followed by an increase in the amount of ‘active’ phloem. In only two genera, Ricinodendron and Tectona, could it be deduced that there was any cessation of cambial activity during the dry season, as indicated by the lack of ‘active’ phloem. In all other cases ‘active’ phloem was present throughout the dry season. The depth of the total fluorescent zone indicates that there is a large amount of phloem produced during the year in many of these trees.Tylosoids were formed in three of the six genera at the time of formation of the definitive callose; in Antiaris and possibly Ricinodendron the tylosoids became lignified, but not in Bombax.