The leaf secretory scales of Combretum molle (Combretaceae): morphology, ultrastructure and histochemistry

This paper reports the results of a study on the morphology, mode of secretion, ultrastructure and histochemistry of leaf secretory scales of Combretum molle using both light and electron microscopy. The density of the secretory scales is higher on the abaxial leaf surface in the intervein areas. Each secretory scale is made up of a basal epidermal cell, a short bicellular stalk and a multicellular umbrella-like head comprising 8-24 cells. The secretion is released from each head cell into the subcuticular space through a lateral ostiole, and then onto the leaf surface via a central pore on each scale. This secretion mechanism is described in this study for the first time in family Combretaceae. Ultrastructural characteristics of scale cells display the typically active metabolism of secretory systems. Preliminary histochemical investigations show that these scales contain lipids, terpenoids, phenolics, flavonoids and alkaloids which probably offer anti-microbial and anti-herbivore protection.