Electron Microscope Studies on the Origin and Development of the Vacuole in Root Tip Cells of Phaseolus

Abstract

1. The vacuoles of Phaseolus root tip cells arise by expansion of small irregular-shaped provacuoles in meristematic cells.
2. A differential staining effect obtained, together with certain morphological features, indicated that provacuoles were not derived from any other cell organelles.
3. Because of this it is suggested that one or more provacuoles persist in the cytoplasm during cell divisions, thus giving continuity to the structures.
4. Provacuoles proliferate through the cytoplasm by extension growth of the surface membranes forming long tentacle-like profiles in the cytoplasm, parts of which expand to produce more provacuoles.
5. Subsequent enlargement of these provacuoles to form the vacuole proper, involves, firstly, active growth of the membrane, and secondly, the interplay of hydrostatic factors.