66 • Temperature and Flowering 



Hippeastrum, for example, also studied by Blaauw (see Went, 

 1948), has no such requirement for a long period of low tempera- 

 ture, and flowers several times a year at high or moderate 

 temperatures. The similarity between the cold requirement in a 

 plant such as the tulip and typical vernalization should also be 

 noted. Here of course the effect is on flower development, not 

 induction or initiation, but the conditions involved and the final 

 results are the same, although the underlying physiological con- 

 ditions are unknown in any case. 



Unlike light or certain chemical factors, temperature cannot be 

 given or withheld but only changed, and it ailects essentially all bio- 

 chemical processes. This makes it at once the most important single 

 factor in development and the most difficult to study in any de- 

 limited way. Hence it is not surprising that terms such as vernali- 

 zation are almost meaningless except to indicate a particular kind ol 

 manipulation, and may not designate any single specific physio- 

 logical process. The brevity of this discussion relative to those on 

 other factors affecting flowering should be taken to reflect not a 

 lesser importance of its problems, but only how little is known 

 about them in any fundamental sense. See Went (1953, 1957) for 

 a much more thorough treatment of the effects of temperature on 

 all aspects of plant growth; a review by Chouard (1960) emphasizes 

 the complexity of vernalization and related low-temperature effects. 



