[Fluorescence-microscopic analysis of pro-buds of moss protonemata stained with acridine orange]

1. Vitalfluorochromation with Acridine orange can be used for selective staining of pro-buds and buds of moss protonemata; the stain appears in the cytoplasm. 2. Differences in the fluorescence of kinetin-induced and non-induced branches are detectable 10 hours after the beginning of kinetin treatment. 3. Using acridine organge (a dye which combines with RNA) an increase in the cytoplasmic RNA content can be shown immediately after the induction of pro-buds. Spontaneous and kinetin-induced buds do not differ in this respect. 4. Kinetin seems to activate the RNA synthesis required for bud formation in many caulonema cells. No activation occurs in all chloronema cells and in some inactive caulonema cells.