TIMING AND THE FLOWERING PROCESS 133 



must be highly accurate, stars must be recognized, and time of year 

 and time during the night must be compensated for by involved 

 calculations. Nevertheless, the entire system for carrying out this 

 intricate procedure is built into the brain of the bird from birth, since 

 birds raised in captivity are quite capable of responding and migrating 

 as well as birds that have already made the trip. 



The ability to train honey bees to feed at a given time of day as 

 well as at a given location may be an example of adding a time memory 

 to celestial navigation. It should perhaps constitute a fifth major 

 category. 



BOnning's Theory of Endogenous Rhythms Applied 

 TO Flowering (1, 8, 12) 



Timing in flowering has been overlooked somewhat in the search 

 for the pigment system, for the flowering hormone, and for other 

 chemical mechanisms. Most workers in the field seemed to feel that 

 timing was merely a matter of how long it took for certain reactions 

 to go to completion. The objective of research was to find the 

 reactions and study them, but nothing out of the ordinary was 

 expected. 



This was upset somewhat by Running, the German botanist who 

 has studied persistent rhythms. He had accumulated an extensive 

 background of information about the endogenously controlled leaf 

 movements in many plants (especially the common bean), and he 

 had developed the idea that these movements went through a two- 

 phase cycle. One phase could be observed at night when the leaves 

 assumed one position, and this Biinning called the skotophile^ (or 

 photophobe) phase. The light phase, when the leaves assumed 

 another position, was called the photophile phase. This description 

 and theory of leaf movements was applied to the flowering process. 

 He said that flowering was promoted if plants were exposed to light 

 during the photophile phase. He had shown that the phases were set 

 in most species when the plant went from the darkness into the light 

 in the morning (some species, including the cocklebur, initiate the 

 cycle upon going from light to darkness). It was postulated that 

 long-day plants had a delayed photophile phase, so that a long period 



8 Usually in America these terms are spelled without the "e" (e.g. skotophil), 

 but the spelling here is probably preferable. 



