The secondary phloem of seven species of woody dicotyledons (Populus deltoides, Quercus alba, Rhus glabra, Robinia pseudoacacia, Salix nigra, Tilia americana, and Ulmus americana) was fixed in glutaraldehyde and in formaldehyde–glutaraldehyde and postfixed in osmium tetroxide for electron microscopy. The pores of the lateral sieve areas are essentially similar in structure to those of the sieve plates, with the exception that many of the lateral sieve-area pores contain median nodules at maturity. In addition, some pore groups in Rhus, Robinia, and Tilia are associated with median cavities, median enlargements arising through the union of two or more median nodules, similar to those associated with the sieve areas of conifers. The lateral sieve-area pores are lined by the plasmalemma and variable amounts of callose and contain P-protein. It has been concluded that the P-protein normally is loosely arranged in the pores.