Fig. 4. Vernalization responses (the difference in number of days necessary to reach Dev49 between unvernalized and vernalized treatments) for the 16 H. vulgare subsp. spontaneum accessions and four H. vulgare subsp. vulgare cultivars listed in Table 1 and grouped in Fig. 2. Panel a shows the average vernalization response of the four groups at each photoperiod regime. Group means followed by the same letter are not significantly different at the 0.05 probability level. Panel b shows the vernalization responses of each genotype at long (18 h) and short (8 h) photoperiod regimes.