Cell wall perforation in the articulated anastomozing laticifers of the opium poppy, P. somniferum L., was examined by EM. Perforation resulted from a gradual thinning of the walls on both sides of the middle lamella. Thinning occurred uniformly over transverse walls during articulation and at localized sites along lateral walls during anastomosis. Electron-dense globular deposits were seen at perforation sites; their function in the perforation process was not apparent. The progressive and simultaneous thinning of the cell wall on either side of the middle lamella at the site of a developing perforation suggests that wall-degrading enzymes (cellulases), rather than pressure, may be involved in the wall-perforation process.