18 THE FLOWERING PROCESS 



flower buds begins to occur as soon as the proper temperature 

 is applied, and in some of these cases if the proper tempera- 

 ture conditions are removed, the development of the flower 

 will cease. Such a response is referred to as being direct or 

 non-inductive. We will arbitrarily restrict the term vernaliza- 

 tion to delayed (inductive) promotion of flowering by low 

 temperature (but see discussion in Chapter 4). 

 ' A. Low temperatures promote flowering. In known 



examples, this is usually, but not always, an inductive 



response. 

 I B. High temperatures promote flowering. This is prob- 

 ably always a direct response. 

 I C. Alternation of temperature promotes flowering. This 



is also a direct response. 

 3. Absolute or qualitative response to temperature. Flowering 

 in such plants is absolutely dependent upon a particular 

 temperature treatment. 

 I A. Low temperature is required for flowering. Called 



vernalization if the response is delayed (inductive). 

 j B. High temperature is required for flowering. Usually 



a direct response. 

 I C. Plants flower only if temperatures are alternated. 



Also direct. 



in. Interactions between Temperature and Photoperiodism 



1. No qualitative change of day-length response type due to 

 change in temperature. 



A. No known interaction with temperature. Of course, all 

 day-neutral plants would fit in this category, but placement 

 of other plants in this category usually implies only a lack 

 of study. It seems quite likely that any such photoperiodi- 

 cally sensitive plant which is studied in sufficient detail 

 would prove to have some sort of interaction between day- 

 length and temperature. It should at least fit in one of the 

 next two categories. The majority of plants listed in the 

 appendix had to be placed in this category, but future work 

 is bound to change this situation. 



