I always found that a few of my Aussie native dens have a very interesting
velamen in that they turn splotchy when wet. They appear as mostly white,
but have a few green spots.

Kye.

"Ray B" wrote in message
news:0XQ9i.13456$Gy4.3106@trndny08...
An interesting question, Bob.

I see something similar, and I grow in a greenhouse, so the humidity is
usually quite good. I have always chalked it up to individuals, rather
than type of plant, but maybe I just didn't catch the connection.

The velamen is supposed to capture water, and I had never heard of the
"prevent moisture loss" concept applied to it.

Might it have something to do with age, or maybe what the conditions were
like when the roots grew? The concept there is that maybe - if the plant
was watered well during the time of the growth of those specific roots -
the velamen was not a crucial part of the uptake mechanism, so didn't
develop to absorb as readily as that that grew under drier conditions.
--

Ray Barkalow - First Rays Orchids - www.firstrays.com
Plants, Supplies. Books, Artwork, and lots of Free Info!


"bobc" wrote in message
ups.com...
I was re-reading previous posts on Renanthera and the discussion
wandered into watering aerial roots. Several people mentioned roots
turning green.
I have noticed that some of my plant's roots turn green instantly and
others take a much longer time. Some do not turn green at all.
Neostylis, Christieara and Phalaenopsis are in the former group. As
soon as water hits them the roots begin to darken. Dendrobium
biggibum, Sophronitis cernua and Laeliocattleya Little Stars only get
some green patches ( at best), even after fifteen or twenty minutes in
a bucket of water. They all look fine, making new growth and
flowering regularly.
I'm wondering if because of the low relative humidity in my
conditions, the velamen on certain plants becomes less permeable,
protecting against water loss? With the consequence of making it
harder to absorb water?
Neostylis, Lc and the Phals are potted in bark, while Den. and Soph.
are on bark mounts with a wee bit of sphagnum moss. The Christieare
is in a basket with several large chunks of bark.
I'm wondering if those of you with greenhouses also observe this
phenomenom?
What about Those of you who grow outside all year? ( I'm not angry
because you can - I'm angry because I can't! --- LOL)
Thanks for letting me share!
Bob Campoli - Philadelphia, Pa - growing plants on a windowsill.