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Fuzzy stems. Why?

David Kirschtel kirschte at msu.edu
Mon Nov 20 16:54:30 EST 2000

Monique Reed wrote:

> Hairs on a stem or leaves can a)provide insulation b)make the air
> layer around the plant more turbulent and slower-moving so water loss
> is less, 

I'd have to take issue with this. If the hairs a far enough apart to
induce turbulence then the result will be to decrease insulation and
increase water loss. Turbulence is a mixing phenomenon. In a fully
developed tubulent flow profile there is effectively zero velocity
gradient, the average velocity next to the surface will be the same as
at all distances from the surface. The innerlayer/ viscous sublayer/
boundary layer has been eliminated. This region of relatively stagnant
air near the surface is what provides the insulation. If on the other
hand the hairs are relative densely packed they will produce skimming
flow over the top of the hairs, effectively creating a new elevated
surface and extending the region of stagnant air around the surface of
the plant. This is what will increase insulation and reduce water loss -
the absence of turbulent flow near the surface of the plant. 

      David Kirschtel * kirschte at pilot.msu.edu * 517.432.0898
    112 N Kedzie Lab * Mich State Univ * E Lansing, MI * 48824

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