EXPERIMENTAL SEPARATION OF CELL DIVISION AND SILICA SHELL FORMATION IN CYCLOTELLA CRYPTICA

1. Cytokinesis is inhibited in Cyclotella cryptica, when the cells are subjected to Ca++ or Mg++ deficiency. As a result of such inhibition, two lateral silica shells are formed. These shells surround the cell cylinder of the diatom at the median region between the intercalary connecting bands. 2. Lateral silica shells are distinguished from the normal valves by being slightly rolled and having their marginal region flattened. Both kinds of shells possess the same type of fine structures. 3. Mitotic inhibition through colchicine induces more than one pair of lateral silica shells which appear on the undivided giant cells showing plasmatic growth. Similar giant cells with many lateral shells are produced in the presence of β-phenethyl alcohol. 4. It was concluded that neither the achievement of cytokinesis nor mitosis are prerequistes for lateral silica shell formation. It is rather dependent upon plasmatic growth. © 1968 Springer-Verlag.