A hypothetical plant growth substance that, it has been suggested, is formed in meristematic regions of a plant subjected to cold. Experiments that apparently show this substance can be transmitted to other plants by grafting have probably failed to separate the effects of photoperiod from those of vernalization. Thus the transmitted flower stimulus could be *florigen
rather than vernalin. Other experiments suggest that, if such a substance is formed, it is only transmitted to other cells by cell division. Thus if one apex on a plant is locally vernalized, the other apices remain unvernalized. It is probable that there is no one substance formed by vernalization and that the biochemical basis of vernalization is different in different cold-requiring species. Thus applying gibberellin to seeds replaces the vernalization requirement in some species but not others. Other substances that have partly or completely replaced the vernalization requirement in different species include auxin, kinetin, RNA, and vitamin E.