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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