Jim Lewis wrote:

On 12 Jan 2005 at 6:21, Nina wrote:

This whole thread confused me, but kitsune's modified ascii
graphic has finally clued me in. From what I know about root
formation (not that much, but I did have a plant physiology
course once.... decades ago), there is no reason you can't get
two areas of root formation on the same branch. It happens all
the time on shrubs that "scramble", that is, that root on low
branches that touch the ground.


Ahh, but these are different. There's nothing inhibiting the 2-
way flow of plant juices as there is in a layer where you've used a
tourniquet or have cut away a ring of bark through the cambium.

But in the instance, there is neither tourniquet nor a ring of bark
cut. It's a saw cut partway through the branch from beneath. The bark
is interrupted only on the bottom of the branch, so "plant juices" can
still flow along the top.

I almost always use the ground-layering method on azaleas and have
gotten several plants off one stem, though some of them were pretty
short. ;-)


Roots that emerge from stems are called "adventitious roots" and
form from the inner bark layer. The formation of these roots are
influenced by hormones (auxin and ethylene) and energy (sugar).
Ethylene is produced by (among other things) wounding, so the
combination of making a wound and keeping it smothered in
sphagnum will allow ethylene to accumulate. Sugar and auxin will
come down from the branch tip. In a normal single girdle
air-layer, sugar and auxin will accumulate in the "upper lip" of
the girdle (unable to go any farther because the phloem has been
severed), and roots formation will be in that upper lip. In a
double girdle such as Kitsune has diagrammed, the lateral branch
between the two girdle sites has been transformed into the new
"apical tip" for that segment, and sugar and auxin should travel
pretty uniformly to both girdle sites. Hope that makes
sense.....

Actually, it isn't a full girdle. The cuts are sawn upwards partially
through the branch but the remaining bark is left intact. So the
upward-growing branch and the the parent branch are both still
maintaining sugar and auxin movement during the layering process.

Uhm . . . ?

However, anyone is free to try this method and report back to us.
(hint)

Already did.

Pastorio

I'M not brave enough to do it on anything I want to keep.

Jim Lewis - - Tallahassee, FL - Nature
encourages no looseness, pardons no errors. Ralph Waldo Emerson

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