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SummaryShoot apices of Lotium temulentum plants exposed to 1 long day were harvested at the beginning of the long day, and on each of the five following days. Longitudinal sections were stained for DNA (Feulgen), DNA and RNA (methyl greenpyronin or acridine orange fluorescence), or basic nuclear proteins (ammoniacal silver nitrate, fast green, or bromophenol blue, with or without acetylation or deamination).The first sign of inflorescence initiation was the localized increase in RNA in pockets of epidermal and hypodermal cells centrally placed between the leaf pri. mordia. This was apparent within 24 hr after the floral stimulus reached the shoot apex, and increased sharply during the next 24 hr. This localized RNA increase was accompanied by an increase in the size of nuclei and nucleoli, and by greater hetero· geneity within each nucleus in the density of DNA and histone staining at the activated sites which give rise to the spikelet primordia.No evidence was found of a fall in histone content, or of an increase in cytoplasmic histone staining, either in the apex as a whole or at the sites of spikelet differentiation, at any time. With all histone stains the pattern was closely parallel to that for DNA, except in one important respect, namely that the arginine-rich histones appeared to be almost completely absent from nuclei from the summit and flanks of the apex, although high in the central core and at the base of the apex.The nature of floral induction, the origin of spikelets, and their morphogenesis are discussed in terms of these results.