HISTORY OF RESEARCH IN VERNALIZATION 



by 

 R. O. Whyte 



Commmwealtk Bureau of Pastures and Field Crops, Aberystwyth 



Introduction: — It requires to be stressed at the outset that the treatment and 

 responses associated with the term "vernalization" represent only one aspect of the work 

 on the developmental physiology of plants, which is receiving the attention of many 

 research workers at the present time. Research on developmental physiology may be 

 said to have begun with the experiments of Klebs in the years up to about 1918. Earlier 

 experiments had been made, but Klebs may be regarded as the initiator of the modern 

 extension of this branch of plant physiology, the main thesis of which is that it should 

 be possible to control and direct the processes of growth and development of a plant 

 by exposure under artificial experimental conditions to the particular factors of environ- 

 ment to which it is exposed in the cultivated field or greenhouse or in nature. 



In this research on developmental physiology, reviewed by the author elsewhere 

 (Whvte, 1946), it appears that the decisive factors of the environment which control 

 growth and development are temperature and light (its presence or absence), and that, 

 once these factors have had an opportunity of operating to the required degree, a further 

 set of conditions, including such factors as the relationship between carbohydrate and 

 nitrogen, water relations, general nutrition and so on, then operate and determine 

 whether a plant shall ultimately exhibit vegetative growth or reproduction (develop- 

 ment). 



A plant displays the capacity to respond to the temperature of its environment in 

 certain instances remarkably soon after fertilization, within 5 or 6 days in one case 

 studied. This capacity is progressively lost with approaching dormancy, and is reac- 

 quired when dormancy of the ripe seed is broken and germination begins. .■\s soon as 

 chlorophyll is formed in the leaves of the young seedling, the light regime of the en- 

 vironment can begin to operate, and from then on the behaviour of a plant appears to 

 depend upon the interrelationship of these two factors, temperature and light. Plants 

 such as winter cereals proceed most rapidly to reproduction if they are first exposed 

 to a certain quota of low temperature, followed by an exposure to a sufficient number 

 of days of the appropriate length, together with an optimal temperature. 



The terms of reference of this article limit consideration to the acquisition by 

 germinating seeds or young seedlings, either in their natural environment or under 

 experimental conditions, of that particular dose of low temperature under the influence 

 of which they can proceed most rapidly and efficiently to reproduction, provided the 

 environment to which they are subsequently exposed is optimal for the reproductive 

 processes of that variety. It is therefore necessary to ignore the wider questions 

 relating to the effect of temperatures at all stages of a plant's life on its reproductive 

 behaviour. The effect of temperature on the photoperiodic reaction of plants is being 

 discussed by Murnekk (pages 39 et scq.). From investigations of plant growth 

 and development such as those being conducted by Went at the California Institute of 

 Technology, Pasadena (1943, 1944a, 1944h), a much fuller understanding of the sig- 

 nificance of temperature will be forthcoming; using air-conditioned greenhouses, it is 

 now possible to maintain the total environment under control throughout the life of 

 a plant, from fertilization to seed formation. 



Taking again the example of winter cereals in the latitudes in which they are cul- 

 tivated, it has long been the practice to arrange their sowing dates in such a way that 

 they are exposed while in the field to the low temperatures desirable, but apparently not 

 obligatory, for progress to reproduction. If these varieties are sown in spring alongside 

 the spring varieties, differentiation of flower primordia may occur after a considerable 

 period of time, but earing does not occur normally. It was the aim of the chillers of 



