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Hello,
From my experience.
When I buy Cryptocorynes in a shop
they have very long petioles
but in my well ligtened aquarium they
become very short
Marek
----- Original Message -----
From:
t*@us.henkel.com
To: aroid-l@gizmoworks.com
Sent: Friday, March 14, 2008 7:39
PM
Subject: [Aroid-l] Phototropism
Dear List,
As many of you know, from time to time I
come across a botanical thought that perplexes me. Today's thought concerns
phototropism, that stalwart of Botany 101 students worldwide. The aroids I
grow (Cryptocoryne) often have very elongated, rather weak petioles. When
growing in crowds (their typical habit) the crisscrossing petioles and leaves
make for a veritable swarm of vegetation floating on water surfaces. Among
this leafy mess is considerable movement on the time order of days. A
time-lapse movie of a patch of Crypt leaves would be a seething turmoil. It is
only because of our own time sense that plants seem to be passive, quiescent
beings.
I assume that much or most
of this movement pertains to the struggle for light. A new leaf emerges and
starts to shade out some existing ones, which then bend and turn to avoid the
dreaded shade. I figure this is a manifestation of positive phototropism, the
leaves seeking to maximize their uptake of light energy. Fine.
Every once in a while I have to manage
the plants and I can never seem to get all the leaves back in a situation
where the upper surfaces are happily pointed to the sky. Some leaves always
get turned over because the petioles are soft and can twist, exposing the
underside of the leaf to the sky and the incoming light. While you can see
that the plants attempt, in their way, to get the leaf turned back the right
way, often this is not possible. Even though the leaf is bathed in light, this
light is shining onto what is anatomically the underside and the plants do not
like it this way. If the leaf does not get turned back upright, it dies. Why
is that?
My first theory is that
it has something to do with stomata, those little openings with which plants
maintain their air/moisture balance. Everybody from Botany 101 knows that the
bottom side of the leaf is where the lion's share of these gizmos lie. If the
underside is exposed to the sun and weather the leaf gets off-kilter and the
plant shuts it down. That's a pretty good theory even if we are dealing here
with aquatic plants where the relative humidity (at least in my setup) is
100%.
My second theory is that the
photosynthetic apparatus in plants is directional, meaning that reception of
photons for photosynthesis is a one-way mechanism. By this theory photons
coming in through the backside, as it were, are not efficiently captured,
basically rendering it the same as if that leaf were in the dark. A leaf in
the dark is a wasted leaf, so the plant gives orders to withdraw the
sap-soluble goodies and abandon that leaf in favor of producing a new one that
can orient itself properly.
Any
ideas from the botanists?
Ted.
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