The development of the torus in the wood of Osmanthus americanus was investigated using transmission and scanning electron microscopy. Torus formation on either side of the pit membrane did not begin until after the development of the associated pit border was well underway. No plasmodesmata were encountered in the torus at any time during its ontogeny. Synthesis of torus material was correlated with a mass of randomly oriented microtubules and dictyosome vesicles. The two halves of the torus did not develop synchronously; deposits of torus material were evident first in the older of two adjacent cells. Selective hydrolysis of the matrix material of the margo also began fIrst on that side of the pit membrane associated with a mature tracheary element. Evidence is presented for a fibrillar as weIl as a matrix component in the torus.