neutral density film

Bill Williams bwilliam at
Fri Jul 2 10:30:08 EST 1993

In article <1993Jun30.155018.17441 at> Tracy Ching,
tching at target.uucp writes:
> 	Pardon the rookie question, but...  What is the R:FR ratio?

It stands for "Red:Far-Red Ratio."  Many plant responses to light, such
as etioloation (remaining white, tall, and spindly, as plants that are
grown in the dark), ratios of different kinds of chlorophylls, and a
whole host of others, seem to be dependent on red (around 660 nm) and
far-red (730 nm) light.  The photoreceptor responsible is called
"phytochrome," and its discovery, history, physiology, and molecular
biology are the stock in trade of undergraduate plant physiology
courses.  Phytochrome responses can be quite complicated, but probably
the most important responses in light-grown (therefore "normal") plants
are to the ratio of light at 660 to light at 730.  Check out a plant
physiology textbook for the phytochrome story -- it's really quite
fascinating.  There's a very nice, readable, but a bit dated treatment
of phytochrome in "The Life of the Green Plant," by Galston, Davies,
and Satter (1980, Prentice-Hall).
William E. Williams, bwilliam at
Divison of Natural Sciences and Mathematics
St. Mary's College of Maryland
St. Mary's City, MD 20686

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