SCANNING ELECTRON MICROSCOPY AND ENERGY DISPERSIVE X-RAY ANALYSIS OF CHALK SECRETING LEAF GLANDS OF OF PLUMBAGO CAPENSIS

Chalk secreting leaf glands of Plumbago capensis Thunb. were examined by polarized reflected light microscopy, scanning electron microscopy, x-ray diffraction, and energy dispersive x-ray analysis. There are about 23 glands per mm² on the lower leaf surface and none on the upper surface. Each gland measures 20–30 μm in diam and consists of four small secretory cells surrounded by four subsidiary cells. Secretion of chalk is apparently through a pore in the surface of each secretory cell. The secreted material was crystalline and x-ray diffraction confirmed the presence of two minerals: calcite (CaCO₃) and nesquehonite (MgCO₃ · 3H₂O). Energy dispersive x-ray analysis revealed the presence of magnesium, silicon, phosphorus, sulfur, chlorine, potassium, and calcium in the epidermal cells. However, only calcium and magnesium and traces of silicon were detected in the secreted material. A distribution analysis showed calcium and magnesium to be uniformly distributed through the secreted material.