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Fuzzy stems. Why?

Darren Obbard darren.obbard at plants.ox.ac.uk
Tue Nov 21 14:22:54 EST 2000

(difficult to follow who said what thanks to the posting order)

> > > 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,

> > [snip: turbulence decreases boundary layers, and thus water loss

> Well, now we know what happens when they don't make botany and
> horticulture students take physics...

No, he was perfectly right (if I've read the order correctly),

There are 4 likely reasons for hairs on leaves/stems

1) Hooked, barbed, poisonous, sticky or just plain awkward hairs (trichomes)
to deter predators

2) Denser long pale hairs to reflect light

3) Dense hairs to extend the boundary layer (insulate) and thereby reduce
water loss (or in some cases heat loss)

4) Sparse hairs to increase turbulence and disrupt the boundary layer at
lower air movement, thereby increasing water loss (and increasing cooling
effects thereof, assuming the plant can afford to spend water on cooling )
and increasing CO2 diffusion into the leaf (probably only relevant in dense
stands of very fast growing material, on a still day)

Darren Obbard
The Queen's College
Oxford OX1 4AW

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