SUMMARY
The utilization of the silver impregnation technique for the nucleoli staining in plant cells allowed us to carry out morphological observations on the nucleolus in vegetative hyphae of Penicillium sp.
Under light microscope the vegetative nucleus shows an argentophilic body of about 0.5–1 μ in diameter, which is located in a peripheral position. Within the nucleus and in close relation with the nuclear envelope, the electron microscope shows a compact structure composed by granular and fibrillar elements. The features of these bodies observed under light and electron microscopy suggest that they represent true nucleoli, resembling typical nucleoli in higher plants.