Abstract

<jats:p> Differentiation of vessel elements in corn is accompanied by marked changes in nearly all organelles except plastids. The young cells increase in volume and apparently synthesize new cytoplasmic protein. The initiation of wall thickening is accompanied by an aggregation of microtubules in specific locations and an increase in the number of mitochondria and dictyosomes. During the period of active wall deposition, the endoplasmic reticulum (ER) shows a highly elaborate form, harbors intralamellar tubules, and nearly blankets those parts of the wall which remain unthickened. Dictyosomes seem to produce at least two types of vesicles, one of which may serve as a carrier of lignin precursors. The final autolysis involves a progressive removal of vacuolar membranes, plastids, dictyosomes, vesicles associated with secretion of noncellulosic polysaccharides, microtubules, and finally plasmalemma, parts of cell wall, and cytoplasm. Mitochondria and ribosomes are degenerated. The ER probably plays an important role in this autolysis. The parenchyma cells associated with vessel elements are rich in mitochondria. </jats:p>