Vernalization and Photoperiodism — 18 — A Symposium 



may be brought to flowering even under continuous illumination and 

 high temperatures. Having found that winter wheat can pass from the 

 vegetative to the reproductive state most readily under the influence of 

 different external factors, in particular low temperature and short day oper- 

 ating alone or in combination, Voss suggests a new definition for '"winter 

 wheat" and "summer wheat." Wheat varieties which, under a constant 

 high temperature (approximately 20° C), constant illumination (by natural 

 or artificial light not exceeding 1500 lux), and otherwise favourable con- 

 ditions in a greenhouse, do not begin to shoot within 4 to 6 weeks are de- 

 scribed as winter wheats. 



Great Britain : — The chief work on the vernalization of cereals in 

 England began about 1931 at the Research Institute of Plant Physiology, 

 Imperial College of Science and Technology, London and 1934-35 at the 

 School of Agriculture, Cambridge. Bell (1935, 1936) worked at Cam- 

 bridge with wheat, barley and oats, but the experiments were not continued 

 and Bell has since investigated the developmental physiology of sugar beet 

 (see Bell and Bauer, 1942, and Whyte, 1946). In his work on cereals, 

 an acceleration in earing was observed in the winter varieties of barley and 

 wheat but none in the oat varieties. Many of the varieties giving the great- 

 est response in the early stages (more rapid germination) showed no ac- 

 celeration in earing, and conversely the winter varieties in which vernaliza- 

 tion produced the maximum difference in earing date showed little or no 

 early response. The type of response is a varietal character. 



Following upon these experiments, a series of sowings was made with 

 vernalized and untreated seed of winter and spring varieties of barley, 

 wheat and oats, one in October and six successive ones in the following 

 spring between Mar. 8 and April 5. The treatment consisted of exposure 

 to 3°C. for 14 days. All but one of the varieties showed a slight accelera- 

 tion in germination. The acceleration in earing was slight or nil in the 

 autumn sowings, but in the spring sowings there was a progressive increase 

 in acceleration with delay in sowing in the winter varieties and, conversely, 

 a progressive decrease in the spring varieties. This difference in behaviour 

 is attributed to the rise in temperature with progressive lateness of sowing ; 

 greenhouse sowings under higher temperature came into ear sooner than 

 field sowings in spring varieties and later in most winter varieties, showing 

 that low temperatures in the open had effected a certain amount of vernaliza- 

 tion. Examination of growing points was also made in these trials and re- 

 vealed great differences in varietal behaviour. 



The long series of experiments made by Gregory, Purvis and other 

 workers of the Research Institute of Plant Physiology, Imperial College of 

 Science and Technology, South Kensington, has provided valuable data on 

 the fundamental biological processes concerned in the response of growing 

 seed to vernalization. The work on effects of temperature during germina- 

 tion was embodied in a publication (Purvis 1934) on the analysis of the 

 influence of temperature during germination on the subsequent development 

 of certain winter cereals and its relation to the effect of length of day. 



Winter rye (var. Petkus) was the experimental material used. One 

 series was grown in normal long day at high and low levels of nitrogen sup- 



