The fine structure of the protoplast in primary tracheary elements of the cucumber after plasmolysis

A striped pattern consisting of lighter and darker bands can be seen under the light microscope on the surface of the cell in tracheary elements in the hypocotyl of the cucumber. After plasmolysis, a striped pattern can also be observed both on the surface of the protoplast and on the cell wall. The nature of the striped pattern on the plasmolysed protoplast was investigated by electron microscopical examination. In the non-plasmolysed cell, high densities of cisternae of the endoplasmic reticulum and of Golgi vesicles are found in the areas between the developing cell wall thickenings. At the same time, bands of microtubules are present along the plasmalemma around the thickenings. Comparing these results with the electron microscope picture of the plasmolysed cell, the following observations can be made: 1. the regular distribution of the endoplasmic reticulum and the Golgi vesicles has disappeared; all cell organelles are disorganized. 2. The bands of microtubules are still present at their original sites. 3. The surface of the plasmolysed protoplast does not become smooth after detachment from the cell wall. It shows low, somewhat irregular ridges. These ridges are the areas which were originally located between the thickenings. Several hypotheses which might explain the pattern observed under the light microscope are discussed.