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In the course of an experimental study of phototropism in seedlings (1, 2) attention has been directed to the plastids as possible participants in the light-detection process. This led to a microscopic study of the cells of the oat coleoptile and thence to the discovery of the body which is the subject of this note. The materials were chosen for their phototropic sensitivity. Avena sativa (oats) var. segerhavre (Victory) coleoptiles, grown in the dark after being given 5 hours' red light from the initial soaking, were used when 25 to 35 mm long. Hordeum vulgare (barley) and Zea mays (corn) coleoptiles, also grown in the dark, were used at the same length; the corn was given 3 hours' exposure to red light at the start. Phycomyces blakesleeanus was grown as described by Gruen (3) and harvested in stage 4. Subepidermal cells of the Avena coleoptile, especially at and near the apex (0.1 to 0.5 mm from the tip), contain a number of small bodies, a little less than 1 # in diameter. Each body consists of a single (probably 3-layered) membrane (Figs. 2 to 5) enclosing a matrix denser than the ground cytoplasm of the cell. In this matrix is embedded a single, usually rhomboidal, crystal; the outline of the crystal is sometimes irregularly polyhedral, occasionally rectangular or even hexagonal. Since the lattice lines sometimes appear to cross at right angles, it is not excluded that the crystal packing may be cubic. Usually the crystal is free from the membrane, but in a few cases it appears attached or adherent at one or more sides, and little or none of the matrix may be present at those sides (Fig. 2). In only one instance has any other defined structure appeared in the matrix, and in this case the included material was not lamellar. Thus, a clear distinction exists

ON A CRYSTAL-CONTAINING BODY IN CELLS OF THE OAT COLEOPTILE