SUMMARYThe structure of the roots of Avicennia marina (Forsk.) Vierb., a salt excretor, and Bruguiera gymnorrhiza (L.) Lam., an excluder (non-excretor), differed in tbe lengtb and tbickness of tbe root cap, pbenolic content, tbe development of tbe Casparian strip in tbe endodermis and in the differentation of tbe vascular tissues.The uptake and distribution of lantbanum, used as a marker for ion movement differed in the two species. Tbougb botb bad similar root concentrations, tbe amount of lantbanum in tbe leaves of Avicennia marina was significantly bigber tban tbat in stem and root, wbereas in Bruguiera gymnorrhiza it was significantly lower. Tbe barrier to lantbanum transport, probably located in tbe bypocotyl, is discussed in relation to tbe anatomy of tbe root and tbe uptake of salt under natural conditions.

Croton gratissimus (Lavender croton) possesses three distinct secretory structures. These include lepidote and glandular trichomes and non-articulated unbranched laticifers. The lepidote trichomes form a dense indumentum on the abaxial surface of the leaves and canopy the glandular trichomes. Although assumed to be non-glandular, transmission electron microscopy (TEM) indicated high metabolic activity within the stalk and radial cells. Glandular trichomes are embedded in the epidermal layer and consist of a single cell which forms a prominent stalk and dilated head. Laticifers occur on the mid-vein of leaves and are predominantly associated with vascular tissue. In the stems, laticifers are associated with the phloem and pith. Both trichome types and laticifers stained positive for alkaloids, phenolic compounds, and lipids. Positive staining for these compounds in lepidote trichomes suggests their involvement in the production and accumulation of secondary metabolites. These metabolites could provide chemical defense for the plant and potentially be useful for traditional medicine.