Effect of Temperature
Certain plants such as the winter rye (Secale cereale) and the biennial strain of henbane (Hyoscyamus Niger) require exposure to low temperature conditions before they start flowering. A phenomenon known as 'vernalization' or 'Yaronization' was noted by the Russian Plant physiologist Gustav Gussner in 1915. Here also embryo or shoot apex seems to be the site of perception and the role of a hormone 'Vernalin" is suggested. Unfortunately like florigen, vernalin has been still elusive. Gibberellin treatment is known to substitute for cold treatment.