THE LOW TEMPERATURE PROMOTION OF FLOWERING 55 



10 12 14 



WEEKS OF VERNALISATION TREATMENT 



Figure 4-2 

 Final relative flowering response to diff'erent vernalization times. 

 Curve 1 represents results with intact grain; curve 2 with excised 

 embryos provided with 2 % sugar ; and curve 3 excised embryos without 

 added carbohydrate. Data from Purvis (31). Compare the shape of 

 these curves with the autocatalysis curves shown in Fig. 10-3. 



temperature is about 20°C. Temperatures below this promote 

 flowering, and temperatures above tend to nullify the effects of a 

 low temperature treatment. The devernalizing high temperatures 

 must be applied within a relatively short time after the cold treatment. 

 Usually a period of 3 to 5 days is sufficient to stabilize the vernalized 

 condition so that devernalization fails. 



In some early experiments of the English workers, devernalization 

 was brought about by drying and storing vernalized seed. Apparently 

 this was because the seeds were not dried as thoroughly as they 

 should have been. Nevertheless, the reversal to the unvernalized 

 state was quite evident and beyond question. 



6. Vernalin 



In the laboratory of Melchers, it was possible to graft a vernalized 

 henbane plant to a nonvernalized plant, causing the nonvernalized 

 plant to flower. Thus Melchers suggested that a substance, which he 

 called vernalin, was produced by the process of vernalization, and 

 that this substance would pass across a graft union. Comparable 



