Fluorescence microscopy of Douglas-fir foliage epiflora

Douglas fir needles stained with the fluorescent dye, primulin, were observed microscopically usingepiillumination with a mercury arc light source. Microorganisms fell into three categories: algae, whichexhibited primary fluorescence; actinomycetes and fungi, which exhibited the secondary fluorescence ofthe adsorbed dye; and darkly pigmented fungi, which appeared black on the background of the fluores-cing Douglas fir needle. A scanning electron micrograph is included for the purposes of comparison.