tapetum A layer of cells, rich in food, which surrounds the spore mother cells in Tracheophyta (e.g. in the pollen sacs of the anther in a fern sporangium). This layer may either break down to form the periplasmodium, a fluid that is absorbed by the developing microspores, or it may last longer, breaking down shortly before anther dehiscence and secreting substances into the locule.

tapetum In many nocturnal mammals, a layer of cells either in the retina or outside it, in the choroid (e.g. in cats), that contain crystals of zinc and a protein (often riboflavin, which fluoresces). The tapetum reflects light back through the retina and so increases the sensitivity of the eye to dim light. At night, when the pupil is fully dilated, reflected light from the tapetum will cause ‘night shine’ if the animal turns to look in the direction of a sudden bright light (e.g. car headlights).

tapetum In many nocturnal mammals, a layer of cells either in the retina or outside it, in the choroid (e.g. in cats), which contain crystals of zinc and a protein (often riboflavin, which fluoresces). The tapetum reflects light back through the retina and so increases the sensitivity of the eye to dim light. At night, when the pupil is fully dilated, reflected light from the tapetum will cause ‘night shine’ if the animal turns to look in the direction of a sudden bright light (e.g. car headlights).

tapetum A reflecting layer, containing crystals of guanine, in the choroid of the eye of many nocturnal vertebrates. It reflects light back onto the retina, thus improving vision and causing the eyes to shine in the dark.