THE LOW TEMPERATURE PROMOTION OF FLOWERING 47 



promotion of flowering by low temperature. In Chapter 2 this 

 practice was followed. First a distinction was made between causa- 

 tive effects of temperature on flowering (the response seems to be 

 caused by the exposure to low, high, or alternating temperatures) and 

 interactions of temperature with day-length (the photoperiodism 

 response is modified to a greater or lesser extent by temperature). 

 Second, a distinction was made between inductive (delayed) or 

 non-inductive (direct) temperature effects on flowering. The term 

 vernalization was restricted to causative, inductive promotions of 

 flowering by low temperature. The term was first formulated in 

 Russia as "jarovization" (jarovizacija). It is based on Latin, and an 

 English equivalent might be "summerization". Vernalization as used 

 in German and English implies "springization", as does printaniza- 

 tion in French. Of course the implication is not that the genetics of 

 the variety is changed to the summer or spring form, but only that 

 the variety is made to act like the summer or spring form in response 

 to an artificial cold treatment. 



In this chapter we will review some of the history of the topic, 

 summarize the principal facts relating to vernalization, discuss some 

 of the recent work with applied pure chemicals and plant extracts, 

 consider some theoretical aspects of vernalization, and examine 

 briefly some work on direct (non-inductive) effects of temperature 

 on flowering. 



Some Historical Background Perspective 



The history of research in this field is worthy of summary, because 

 it provides an excellent example of how quite obvious phenomena 

 may be overlooked or simply considered uninteresting, either because 

 research is being carried on more actively in some other field or 

 because interpretation is held back by the predominance of some 

 incorrect theory which is held in high regard. Thus as our under- 

 standings of chemistry were long retarded by the phlogiston theory, 

 so knowledge about the environmental stimuli which might lead to 

 flowering was held back by preoccupation with the idea that flowering 

 came about in response to changes in plant nutrition. 



Given spring wheat, which flowers a few weeks after planting in 

 the spring, and given on the other hand winter wheat, which flowers 

 by mid-sunmier only if it has been planted the previous fall, it would 



