Darren Obbard wrote:
>> (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
> increases]
>> > 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
> --
> Darren Obbard
> The Queen's College
> Oxford OX1 4AW
Could there be just
5) to increase the surface area (I'm not a botanist, just a thought).
Edwin Hutton
