Unusual cell wall layers in elm parenchyma of secondary xylem

Multilayering of secondary wall layers in American elm parenchyma cells is described. This includes one additional layer like S1–S3 and protective layers each in vasicentric parenchyma and up to two additional such layers in ray parenchyma. These extra layers are comparable with those mentioned by a few other workers, but they are not necessarily related to tylosis formation as implied by some of these.