Adventitious buds are such as are newly formed from callus or other tissues in places not normally provided with buds, as is often seen on occluding wounds - e.g. stool shoots. They may also be developed on roots, a fact utilised in propagating Bouvardias, Horse-radish, etc., by means of root-cuttings, and the suckers of Plums and other fruit trees are shoots springing from adventitious buds on roots.
Adventitious buds are also common on leaves (e.g. Bryophyllum, Ferns, etc.), and are frequently induced on them by wounds - e.g. Gesneria, Gloxinia, etc. Even cut cotyledons may develop them, and pieces of leafless inflorescence (Hyacinth), hypocotyl (Anagallis), and in fact practically any wounded tissue with a store of reserve materials may be made to develop them: thus they have been found arising from the pith of Sea-kale, and are commonly developed from the cut bulb scales of Hyacinths.
Apospory and Apogamy are particular cases of the production of vegetative buds on the leaves in place of sporangia in Ferns (Apospory), and on prothallia in place of Archegonia (Apogamy), in the latter case induced by dry conditions and strong illumination.