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THE FLOWERING PROCESS 



— : — ] — I — \ — I — \ — 1 — : — m — i — i — i — i— i — i — i — i — r 



-6.-4-2 2 4 6 8 10 12 14 16 



TEMPERATURE DURING VERNALISATION TREATMENT IN °C ■ 



Figure 4-1 

 Final relative flowering response as a function of temperature during 

 vernalization. The data represents response of Petkus rye to a 6-week 

 period of treatment. Original data of Purvis and of Hansel (see 31). 



also vary for different species. In a few cases such as summer wheat 

 which has only a quantitative vernalization requirement, 3 weeks 

 seems to be an optimal time. In many other cases (e.g. henbane) 

 the optimal duration may be longer than 3 months. In a few cases 

 such as Petkus rye, an effect can be detected after only 4 days, but 

 with some plants 4 to 8 weeks are required for any effect at all. 

 Figure 4-2 shows results with Petkus rye. Usually treatment dura- 

 tions longer than the "optimum" produce the same effect as the 

 optimum, but in a few instances there seemed to be a slight reduction 

 in flowering with extremely long treatment times, and this was called 

 o vervemalization . 



5. Devernalization 



If the cold treatment is followed immediately by high temperatures, 

 plants revert to the unvernalized condition, in which the cereals 

 flower only after a long time, and the biennials remain completely 

 vegetative and will not flower even on long-days, unless they are 

 revernalized. Fairly high temperatures such as 35°C are most 

 effective, but in rye temperatures above 15°C begin to have a 

 devemalizing effect (see Fig. 4-1), and in henbane the neutral 



