Bill Williams bwilliam at oyster.smcm.edu
Wed Jan 26 12:18:05 EST 1994

In article <adwright.759428326 at vincent2.iastate.edu>
adwright at iastate.edu () writes:

> The open top would allow the normal conditions of humidity over the leaf 
> while you measure the resistance of the other side.  I suspect that a closed
> top could favorably affect the water relations so that the other side of the 
> leaf (that you are measuring) would show decreased resistance. 
> Allen

I would expect this to affect the readings only if you had the
porometer on the plant a loooong time, which would foul up the CO2
concentration, the humidity near the measured surface, and the leaf
temperature, and generally make your readings not very useful.  I
suspect the largest effect would be if the leaf were amphistomous (is
Arabidopsis?) - if the type of lid you use allows transpiration from
both sides of the leaf to be sensed in the chamber -- as some of the
Li-Cor lids do -- then you'd be measuring the parallel conductances of
the top and bottom surfaces.
William E. Williams
Department of Biology
St. Mary's College of Maryland

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