Whyte 



-21 



Research in Vernalization 



supposed to be translocated and accumulated in all growing points of the 

 shoot, and when a critical concentration is reached induces flower initiation. 

 The increasing rate of formation of primordia indicates that the substance 

 increases autocatalytically. In spring rye about 2 weeks at normal summer 

 temperatures after germination suffice to reach the critical level, while in 

 unvernalized winter rye somewhat less than 6 weeks are required. 



(c) An oxidative reaction is involved in the formation of the substance, 

 as anaerobic conditions completely inhibit its production during vernaliza- 

 tion of winter rye and partially so in spring rye. 



During vernalization the "flower-forming" substance or its precursor 

 increases in concentration so that the critical level is reached earlier, and 

 thus spikelet initiation sets in earlier in the sequence of labile primordia, and 

 a progressive reduction in leaf number occurs, finally reaching the minimum 

 of seven characteristic of spring rye. The progressive eiTect of longer 

 duration of low-temperature vernalization can formally be accounted for 

 on these lines. 



The relations to day-length are more difficult to formulate. The out- 

 standing problem here is related to the fact that in both spring and winter 

 rye in continuous short days a maximum leaf number is found, which is 

 approximately constant and independent of temperature of germination. In 

 spring rye the "flower-forming" substance is already present in high con- 

 centration, but only in long days do the early members of the series of labile 

 primordia form spikelets. It appears, therefore, that two stages are in- 

 volved in the process. A precursor depends for its formation on a genetic 

 factor in spring rye and on low temperature of germination in winter rye. 

 This precursor accumulates in all the growing-points, increasing autocataly- 

 tically. A second stage in the process involves reactions depending on day- 

 length. 



The relations were schematically represented as shown below : 



E (leaf-promoting substance) 



Precursor short day 



V < 



>B_^ 



long day 



> 



C- 



->D (spikelet-promoting substance). 



The next experiments reported by Gregory and Purvis (1938a) con- 

 tinued the process of narrowing down the problem of the localization of the 

 vernalization effect. It was concluded that the process of vernalization is 

 localized in the embryo itself and is entirely independent of changes in the 

 endosperm or aleurone layer which may take place during germination. It 

 was therefore concluded that the growing embryo is able to synthesize hor- 

 mones from a simple substratum containing glucose and inorganic salts (in- 

 cluding nitrates), and that Cholodny's interpretation based upon the exis- 

 tence of large quantities of blastanin in the endosperm and the increased 

 transference and concentration of this substance in the developing embryo is 

 inadequate. 



The phenomenon of reversal of vernalization (devernalization) by Jiigh 

 temperature had already been reported by Gregory and Purvis (1936c) ; 



