Fig. 9. Whole-mount staining of control and dimB- mutant standing slugs. dimB- and control (random integrant) strains were created containing ecmAO:lacZ. After development to the standing slug stage, slugs were stained with a blue ß-galactosidase chromogen. Quantitative analysis of additional such images was performed to measure the areas occupied by the prestalk and prespore zones. These measurements were taken from photographic images, using the `magic wand' tool in `Adobe Photoshop' to select areas with similar signal densities. This revealed more heterogeneity in the apparent fraction of prestalk cells in the mutant but, on average, there was no major difference from the control (control=22±4.4%, n=14; dimB null=19±8.9%, n=15). The greater heterogeneity of the dimB-null slugs probably results from their failure to migrate away from their point of origin and from their tendency to break up into fragments. For double staining analysis, dimB- and control (random integrant) strains were created containing a pspA:glucoronidase reporter and one of the three prestalk lacZ reporter fusions indicated at the left. The strains were developed on water agar to the standing slug stage and the slugs were fixed and stained sequentially for ß-glucoronidase (blue) and ß-galactosidase (red).