photoperiodism

Ross Koning koning at ECSUC.CTSTATEU.EDU
Sat Nov 15 17:35:56 EST 1997


At 1:31 PM -0500 11/15/97, Carl Pike wrote:
>In our class discussion of the photoperiodic control of flowering, after I
>presented the experiments showing (by means of night interruption) that
>plants are timing the length of the night, rather than the length of the
>day, a student asked **why** (in an evolutionary sense) it is the night
>that is timed.

My immediate thought is that day is fickle.
A passing thundershower, an eclipse, a passing
animal, these might all interfere with a day-based
seasonal sensing process.  Until the fairly
recent advent of artificial light, night is
far more reliable to help organisms detect
the seasons.  As bright as a comet might be,
and even the phases of the moon, the darkness
of night through millions of years has probably
been pretty steady at a certain threshhold
(full moon).  The sensing mechanism only has
to be less sensitive than the lunar phase changes
to avoid interference and become an effective
"calendar."

My two cents...

ross

_______________________________________________________________
Ross Koning                 | koning at ecsu.ctstateu.edu
Biology Department          | http://koning.ecsu.ctstateu.edu/
Eastern CT State University | phone: 860-465-5327
Willimantic, CT 06226 USA   | fax: 860-465-4479
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