Oliver Sparrow ohgs at chatham.demon.co.uk
Tue Jul 19 02:17:43 EST 1994

I have answered Joe directly: I hope that he received the text. I have an
"orchid" question of my own which fits better here than rec.garden.orchids.

I assert that orchids are C4 plants, although I have no general data on
which to base this. There have been some studies of which I am aware on
the leaf architecture in one genus (Cymbidium) which suggest C4-ery but
I know of no biochemical studies. If known, reference welcomed.

The reason is the following. In the wild, most epiphytic orchids live lives
of sharp extremes. Many environments are strongly seasonal. In addition, 
however, they is a strong diurnal polarity. Epiphytes are commonly baked dry
by midday (water potential in the bark on which they are growing in the order
of -15 to -30 bar, which I did measure, years ago). It may or may not rain 
in the late afternoon but the evenings are damp, misty, dew-sprinkled. Dawn is

I have adjusted my cultural practice to match this: dry days, humid nights.
The results have been spectacular. This would match with a CAM type of 
photosynthesis (or anyway, dark fixation, light energy gathering). Does anyone
have any comment or data?

  Oliver Sparrow
  ohgs at chatham.demon.co.uk

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