• Vernalization (from Latin vernus, of spring; Russian yarovization coined by T.D. Lysenko, 1928) is the acquisition or acceleration of the ability to flower via exposure to prolonged cold temperatures (typically $1^\circ\text{C}$ to $7^\circ\text{C}$).
• It is a vital evolutionary adaptation preventing winter annuals (winter wheat, barley) and biennials (cabbage, carrot, sugarbeet) from flowering prematurely before the onset of winter.
• Stratification is the moist-chilling treatment given specifically to imbibed dormant seeds to terminate embryonic seed dormancy.
• Phototropism and thigmotropism are directional growth movements in response to light and touch, respectively.
• Therefore, the cold requirement for flowering is called vernalization (Option 2).

Vernalization requirement in crops:

• Vernalization is the acquisition of a plant's ability to flower in the spring by exposure to the prolonged cold of winter.
• Winter barley (Hordeum vulgare) and biennials like carrot (Daucus carota) have an obligate or quantitative cold requirement (vernalization) to induce flowering.
• Sunflower (Helianthus annuus) and ragi/finger millet (Eleusine coracana) are tropical/subtropical annual crops that do not require vernalization.