The development of yeast colonies on solid agar substrates served as a model system to investigate the growth of higher fungi in a heterogeneous environment. Applying a new analytical technique - which was based on the estimation of the intensity of transmitted light from microscopic images taken along the colony radius - cell-density distributions inside fungal mycelia were measured at an extremely high spatial resolution. Using this method, the adaptation of yeast colonies to the limitation of different nutrients was investigated. Under conditions of carbon or nitrogen limitation, populations of the dimorphic model yeasts Yarrowia lipolytica and Candida boidinii underwent a transition in their morphology from solid colony to mycelial colony patterns. When grown under conditions that induced the mycelial morphology, colonies extended linearly at a constant rate irrespective of the initial nutrient concentration. In general, the cell density within the population declined at higher degrees of limitation. Nitrogen-limited colonies of both model yeasts, as well as carbon-limited Y. lipolytica colonies proceeded to extend until the growth field was finally covered by the population. Under these conditions, areas of fairly constant cell densities were formed during the growth process. Only carbon-limited C. boidinii colonies stopped extending at a final diameter which was small when compared to the size of the growth field, and formed a cell-density profile which was monotonically declining. The observed differences in the final colony diameter, and in the cell-density profile morphology indicated the presence of different regulatory mechanisms that ruled the colony development of the model yeasts. The presented monitoring technique for the biomass distribution inside fungal populations provided the basis for a quantitative and non-invasive description of mycelial development.