148 the flowering process 



Other Problems Relating to Timing in the 

 Flowering Process 



There are other very important problems in timing besides that 

 relating to the oscillating or hour glass nature of the flowering clock. 



1 . Are There One or More Physiological Clocks in the Functioning 

 Organism? 



More specifically, is the clock that controls leaf movements the 

 same as the one that measures the dark period ? This may prove to 

 be a rather difficult question to answer. We know that there are a 

 number of superimposed rhythms in living organisms. As mentioned 

 earlier, the fiddler crab has daily rhythms superimposed on tidal 

 rhythms which are superimposed on lunar rhythms. We could build 

 a single clock which exhibited a number of different rhythms. Most 

 clocks in fact do. The second hand has a period of one minute, the 

 minute hand has a period of one hour, the hour hand has a period 

 of 12 hr, and we interpret all of this on the basis of a 24-hr period. 

 Indeed some watches give the day of the year and the phases of the 

 moon. Is this analogous to the physiological timing responses, or 

 does each biological rhythm or manifestation have its own time- 

 measuring mechanism ? 



2. Is the Clock Endogenous or Exogenous ? 



The discussions so far have implied that timing is controlled from 

 within the organism in a manner analogous to the measurement of 

 time by a wind-up clock. When the rhythms continue, even though 

 the organism is placed in a non-varying environment, the endogenous 

 clock seems very likely. Furthermore, individual organisms vary 

 from one another in the period of their time measurement. Thus 

 the rats running in their cages were out of phase with each other 

 within a few days. How could they be responding to the external 

 environment when each responds with a different period in the same 

 environment ? 



Nevertheless, Frank Brown (1) feels that time is measured in 

 response to some subtle environmental factor which is not controlled 

 in today's "constant" environment rooms or chambers. He has 

 measured rhythms in rate of respiration of various tissues placed in 

 such rooms, and he finds slight variations in response that are the 



