FIGURE 4. Attachment to a substrate allows a racE null cell to divide. A racE null cell suspended in medium containing less that 0.03% agarose slowly settled onto the substrate. Notice how other attached cells come into the same plane of focus. The racE null cell attempts to divide in suspension by forming a cleavage furrow but it fails and its furrow begins to regress. The cell attaches to the coverslip and becomes 'phase-dark'. Remarkably, the cell quickly forms a new cleavage furrow which constricts to completion.