A form of *tissue culture
in which excised leaves, leaf material, or leaf primordia are grown on a sterile growth medium. Mature leaves can be kept healthy under culture conditions for considerable periods. Leaf primordia have been used to study growth and differentiation processes. Experiments with the cinnamon fern (Osmunda cinnamonea) show that the smallest primordia usually develop into shoots when cultured but, as the size of the excised primordia increases, there is an increasing tendency for them to develop into leaves. This indicates that leaf primordia are not irrevocably committed to becoming leaves until a relatively late stage.