APPENDIX 



Continuing work on the following list has impressed me deeply 

 with its highly tentative nature. Complete reliance cannot be placed 

 on the majority of species as listed. Thus the list has only one real 

 value: to demonstrate to the reader who is first encountering the 

 physiology of flowering, that there is a fantastic diversity of response 

 among the many species which have so far been studied. This is an 

 important conclusion. It indicates the complexity of the flowering 

 process, the number of genetically controlled steps which must be 

 directly or indirectly involved, and it implies an intricate and complex 

 ecology of flowering. 



There are at least three reasons why all but the most thoroughly 

 studied, completely standardized genetic types in the following list 

 must be regarded with some suspicion. 



1. Studies are incomplete. Obviously, there are so many possible 

 simple combinations of day-length and temperature, not to mention 

 changes in day-length and temperature with time, changes in light 

 intensity, light quality, humidity (flowering of one plant is now 

 thought to be controlled by humidity! — P. Chouard, personal 

 communication), etc., that few if any plants have ever been subjected 

 to all of them. Thus future work will probably move many plants 

 to more complex categories. 



2. The genetic variability within species and varieties cannot be 

 overemphasized. In a few cases (e.g. Chrysanthemum) the various 

 responses found within a single species are indicated in the following 

 list. 



3. In many cases where work is adequate and varieties standardized, 

 problems of classification still arise because a response may be some- 

 what border-line in nature. This is illustrated in Fig. A-1 for the 

 long-day response. If the experimenter feels that he has waited an 

 "infinite time" (!), then he can feel secure about assignment to an 

 absolute-long-day category. Obviously there are many possible 

 degrees of a quantitative response, and it may be especially difficult 



Q 



205 



