Vernalization and Photoperiodism — 28 — A Symposium 



recorded, ranging from less than 1 day above the controls in Plumage 

 Archer barley to 4 days in Resistance oats. This acceleration in ear emer- 

 gence although statistically significant is too small to be of practical impor- 

 tance in the climate of Great Britain. A small effect of vernalization was 

 noted on the total number of ears produced, but this was not consistent 

 among the varieties used, some giving an increase, others a decrease, so that 

 the mean overall effect was not significant. 



This experiment, in which a high order of accuracy was attained (S.E. 

 of mean yield per acre less than 2 per cent of the mean), showed an effect 

 of vernalization on grain yield not exceeding 10 per cent in the barley varie- 

 ties, 5 per cent in the oats, and no effect on spring wheat, and of these 

 results only those with spring barley attained statistical significance. 



United States of America: — Reference has already been made to the 

 review on vernalization published by McKinney ( 1940) . The author noted 

 that the majority of investigations outside Russia fail to recognize any great 

 commercial gain to be derived from the application of vernalization to the 

 small grains, rice, maize, sorghum, forage crops and cotton in the regions 

 where these crops are adapted. McKinney believes the general opinion 

 to be that the crop problems can best be solved through developing more 

 adapted genotypes. Some commercial value is attached to the chilling meth- 

 od when used to force flowering in daffodils, Dutch and Spanish iris, and 

 Easter lily. Apart from possible application to seed production in biennials, 

 or in speeding up seed production in genetical and general crop improvement 

 studies, McKinney considers that the relation between temperature, photo- 

 period, intensity and quality of light must be fully understood before satis- 

 factory results can be obtained from the initial chilling. 



McKinney and Sando (1933) themselves conducted experiments on 

 earliness and seasonal growth habit in wheat, finding that sexual reproduc- 

 tion can be greatly accelerated by first subjecting the slightly germinated 

 seeds of winter wheat to low temperatures in the dark for 50 to 65 days before 

 sowing. By growing plants from treated seed subsequently at higher grow- 

 ing temperatures in a long day, it is possible to obtain two or more crops of 

 winter wheat in a year, according to the variety. 



Seasonal growth habit in wheat is considered as an aspect of earliness 

 and lateness. So far as earliness is concerned, McKinney and Sando state 

 that the winter varieties have low temperature and short-day optima dur- 

 ing the initial growth phase, whereas spring varieties have optima at the 

 higher temperatures and the longer photoperiods. "Earliness and lateness 

 of sexual reproduction appear to depend on the interrelation of several char- 

 acters such as the number of internodes per culm, the growth rate of the 

 internodes, the duration of the elongation of the internodes, and environ- 

 mental-response characters which influence the expression of these char- 

 acters." In relating environmental response to number of internodes, 

 McKinney and Sando forecast the number-of-leaves interpretation put for- 

 ward by Gregory and Purvis. 



LojKiN (1936) succeeded in vernalizing Turkey Red and Leaf's Pro- 

 lific wheat by exposure to temperatures of 1 to 3°C., but low temperature 

 did not shorten the vegetative period of the spring cereals, Blue Stem wheat 



