ABSTRACT
Many plants exhibit a requirement for low-temperature treatment (vernalization) before they are induced to initiate flower primordia. Exposure to high temperatures, low light flux, or SD, immediately following low-temperature treatment can prevent thermoinduction (devernalization) in some species and under some circumstances. The length of the chilling treatment and the range of temperatures that are effective vary with species and even with variety. In the best investigated cases it appeared that the most successful temperature is dependent on the duration of the treatment. As a rule the optimum temperature decreases when duration increases. An intervening period at a neutral temperature apparently stabilizes the effect of the preceding chilling treatment and prevents any subsequent devernalization. Fractional thermoinduction, i.e., summation of two subthreshold vernalizing treatments, is not as common as fractional photoinduction because of the variety of devernalizing environmental parameters, e.g., high temperatures, low irradi.
