Non-invasive image analysis was used to record the morphometric characteristics of pro- toplast-derived colonies, as described previously (Anthony et al., 1994b). Petri dishes, each con- taining an agarose layer with dividing proto- plasts, were photographed with an Ilford FP4 film using a Nikon 601 35 mm camera with a 55 mm micro lens (1 s exposure at f16). Black and white prints (4 per treatment) were scanned using an Apple Document Scanner connected to an Apple Macintosh IIci computer. The im- ages were imported into the image-analysis package (NIH Image, Version 1.44) at a resolu- tion of 150 dpi. Protoplast-derived colonies were selected by thresholding populations of which identified two regenerated protoplasts, those giving discrete colonies, and those which had exhibited non-sustained division with insignifi- cant colony formation; the latter were subse- quently eliminated image. from the final thresholded