A great number of seeds are able to form a mucilaginous coat after wetting. The functions usually ascribed to the mucilage are directed towards the maintenance of the species. Because of its capacity to retain water the mucilage may protect the seeds against desiccation, create a suitable environment for its development (Frey-Wyssling & Muhlethaler 1965) and play a role in seed dispersal. Dependent upon the plant species the seeds produce mucilages which consist of neutral polysaccharides or acidic polysaccharides; some of the latter can be associated with cellulose (Aspinall 1970). Electronmicroscopic studies on basil seeds (Ocimum basilicum, Labiatae) have shown that the secondary wall of the epidermis cells of the seed coat is mucilaginous. It contains amorphous material in which microfibrils are present as a densely packed helical ribbon (Sassen & Bekers 1977). Wetting of the seeds causes swelling and extrusion of the amorphous and fibrillar polysaccharides. Globular particles with a diameter of 1.5-4.0 fim present in the lumen of the epidermis cells are extruded together with the mucilage (Sassen & Bekers 1977).