When a young leaf primordium of Dryopteris aristata is isolated on a plug of tissue at any time prior to the formation of a lenticular apical cell, the tissue may be induced to develop as a solenostelic bud instead of a leaf. The result depends on the rate of leaf development. In some apices, leaf determination may take place during the first plastochrone; in others it may be postponed until the end of the third plastochrone. Isolation of very young primordia by deep incisions in close proximity to the primordium may result in the cessation of meristematic growth and the formation of parenchyma. The vascular structure of the isolated primordia and the phyllotaxis of the induced buds are described, and the significance of the findings is discussed.