Whyte 



-25- 



Research in Vernalization 



and is then first formed in the anthers, where a cycle of accumulation and 

 disappearance occurs similar to that in the carpel. 



The shortening of the first leaf after low temperature treatment noted 

 by Thimann and Lane (1938) referred to above, and held by them to sup- 

 port Cholodny's hypothesis, has been shown to be quite independent of 

 the vernalization process, for it occurs equally in spring and winter rye and 

 is a different effect of low temperature. 



It has not been possible to deal in any detail with the differences of 

 opinion between various workers regarding the question of reversibility of 

 vernalization. It has already been noted that plants have been successfully 

 "devernalized" by drying, or by exposure to high temperature or to 

 anaerobic conditions. The latest and confirmatory experiments on dever- 

 nalization by high temperature are reported by Purvis and Gregory ( 1945) . 

 Petkus winter rye was vernalized for 42 days at 1°C. and the seeds were 

 then subjected to a range of temperatures for varying periods of time (tem- 

 peratures, 25°, 30°, 35° and 40°C. ; durations, 1, 2, 3, 4, 5, 6 and 10 days). 

 Petkus spring rye was subjected to similar heat treatments without pre- 

 vious low temperature treatment. Results obtained at 35 °C. are given in 

 table where 'scores' give a positive measure of the degree of vernalization ; 

 other results will be later published in full (the method of scoring is de- 

 scribed by Gregory and Purvis, 1938a ) . 



Purvis and Gregory drew the following conclusion from these data : 



(a) Heat treatment of the seed is without effect on the flowering behaviour of 

 spring rye, thus showing that there is no question of a lethal action. Spring rye heated 

 at 40''C. for 4 days scored 120, substantially the same as at 3S°C. The reduction in 

 score in winter rye is therefore not due to any injury effect, as is claimed by investiga- 

 tors who believe that vernalization is not reversible. 



(b) A progressive and significant reduction in the score accompanies prolonged 

 heat treatment of winter rye. The delay in flowering is then due presumably to the 

 reversal of the vernalization effect. Complete devernalization did not occur. After 

 treatment at 40°C. for 2 days the score was 79 ± 8.0 (four times that of unheated and 

 unvernalized winter rye) whereas a further day at 40°C. killed all the seed. 



In the same experiment, after the preliminary vernalization for 42 days 

 at 1°C. and the subsequent heat treatment as above, the seeds were then 

 revernalized by exposure to low temperature for a further 6 weeks. The 

 effect on ear development is shown in the following table. 



