CHAPTER 4 



THE LOW TEMPERATURE PROMOTION 

 OF FLOWERING 



It is now known that flowering is induced or promoted by low 

 temperature in a great many species of plants (see Chapter 2 and the 

 appendix). As might be expected, there are many manifestations of 

 this response, and physiological and descriptive investigations relating 

 to the phenomena extend into the hundreds. Thus a brief summary 

 limited to a single chapter in a book which emphasized the response 

 to light must be only a review of some of the high points. A number 

 of excellent review articles have recently been written, however, and 

 the interested reader is urged to consult these summaries, where 

 original papers are cited in profusion. In the preparation of this 

 chapter, I have utilized the reviews of Napp-Zinn (24), Purvis (31), 

 and Hartsema (17) in Volume XVI of the Encyclopedia of Plant 

 Physiology (5), the review by Chouard (13) in Volume XI of the 

 Annual Reviews of Plant Physiology, and a less available mimeo- 

 graphed copy of a talk given by Melchers. Work with gibberellins 

 has recently been reviewed by Lang and Reinhard (56). 



Researches relating to the responses of plants to cold caused a 

 gradual accumulation of so much descriptive information that the 

 terminology used to refer to the responses has become complicated 

 and difficult, as each author may suggest new terms and definitions 

 relating to his own findings. In the other direction, a single term has 

 been applied to a number of phenomena which are almost certainly 

 different in a physiological sense. Thus the term vernalization has 

 been used to imply virtually any "positive" plant response to low 

 temperature or any early flowering in response to any environmental 

 variable! A majority of workers now feel that the term should at 

 least be limited to low temperature promotion of flowering, and that 

 it should not be used for other responses such as breaking of dormancy 

 of certain seeds or buds. In addition, many of the scientists presently 

 active in the field prefer to restrict use of the term to inductive 



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