CHAPTER 8 



TIMING AND THE FLOWERING 

 PROCESS 



Men have probably always estimated the time of day and perhaps 

 have awakened at the same time every morning. Many of us manage 

 to wake up a few moments before the alarm is ready to go off. Yet 

 scientific recognition of this phenomenon of biological time-keeping 

 was rather delayed. Rhythmic motions such as the "sleep" move- 

 ments of leaves have been noticed by naturalists for the last three 

 centuries, at least. The cocklebur leaf is relatively erect at midnight 

 and nearly horizontal at noon ; bean leaves are horizontal during the 

 day and in a drooping position at night. It was easy to "explain" 

 these actions as responses to light or temperature differences between 

 night and day, but some investigators did suspect (in at least one 

 case, as early as the seventeenth century) that these rhythmic move- 

 ments were a manifestation of an endogenous or internal ability to 

 measure time. The reason for such suspicions was that some rhythmic 

 phenomena will continue even though the environment is relatively 

 constant. 



Studies on biological rhythms became increasingly detailed and 

 accurate. Garner and Allard discovered photoperiodism in 1920. 

 Special time-measuring phenomena such as the time memory of bees 

 were discovered (see Chapter 1). Finally in the early 1950's the 

 phenomenon of biological time measurement became recognized by 

 a rather large body of biologists. At this time the idea was so well 

 accepted that workers in the field began to speak of the "biological 

 clock". 



The observation which was essential to acceptance of the biological 

 clock idea, was the demonstration that certain time-measuring 

 phenomena (especially the rhythms) would continue even though 

 the organism was held under essentially constant environmental 

 conditions. 



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