Non-invasive image analysis was used to record the morphometric characteristics of protoplast-derived colonies, as described previously (Anthony et al., 1994b). Petri dishes, each con- taining an agarose layer with dividing protoplasts, 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 images were imported into the image-analysis package (NIH Image, Version 1.44) at a resolution 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 insignificant colony formation; the latter were subsequently eliminated image. from the final thresholded