This is confusing because by girdling, aren't we interrupting the phloem completely? How would auxin flow upwards from a branch below when there is no phloem left intact? Or are you talking about on the scale of cells?
Yes, interrupted across the girdle, but remains continuous with anything below. The phloem can carry stuff up/down. It is pressurized by the active loading of stuff from the foliage. Otherwise the stuff just oozes down the tree because of gravity. The active 'life above' signal is auxin handed off from cambium cell to cambium cell that only goes downward toward the roots (Polar Auxin Transport). So, I am suggesting that some auxin with photosynthates gets carried upward to the base of the girdle in the phloem. Then it is the unloading of auxin, in particular, from the phloem into the cambium cells that maintains the 'life above' signal so that we can do air layers. I posit that some varieties don't do so well at carrying stuff upward in the phloem and hence the cambium looses the 'life above'signal and dies. In the process of kicking off, these cells emit an ethylene precursor that gets dumped into the xylem (which in turn signals to xylem parenchyma to seal off the xylem).
I have never heard of using lanolin, what does this hypothetically do for the basipedal flow of auxin? Does this basically just keep the conduits open so to speak?
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Exposed cambium cells seem to
inevitably regenerate phloem and bark if moist (dry, of course, it desiccates) This may be why my attempts to provide auxin artificially failed - the new epiderm won't admit IBA (if so, recutting the bottom of the girdle and reapplying IBA would be the obvious 'fix')? Lanolin or augar pastes are a standard tool in plant biology for administering experimental chemical treatments. Basically they hold a supply of stuff (like a plant hormone) that slowly finds its way out and into the plant tissues to which it was applied - talk to Google.
My problem may have been scraping too much of the xylem away, because within a week the leaves dried up. It wasn't until a couple months later that I noticed the bark turning black (codit response) which totally makes sense. I actually remember having a hard time making the cut because of so many branches originating from the trunk where I was cutting. I always try to make my cuts right at or just below a node just for the reason of more activity physiologically in the plant.
I've had this happen when I tried to make approach grafts with 1/8th inch-ish stems and scraped away the bark and cambium on the 'inside' so the 'approacher' (for lack of a term; it isn't a 'scion' per se, nor a thread) wouldn't push out of the groove. After a few days the brown/black bark of cambium death ... (and you know the rest). So, definitely, cutting away too much xylem can also be a problem.
As my previous diatribe outlined, I think it important to make the girdle just above a node, not just below. The remarkable thing is that roots can be generated from cambium/pericyle
anywhere. Vegetative buds, on the other hand, only occur at nodes. The two (buds, roots) have no direct relatationship. An excess of auxin primes any cambium paricyle tissue to become a root tip. While I may be deluded, I do believe this is fact and that it is the singular most significant thing (I think) I've learned in about a decade of messing with woody plants.
I may try cutting "windows" through to the xylem instead of completely girdling the trunk, any thoughts on this? I guess the trick would be initiating root development instead of just callus formation...
Windows have never worked for me. With most a.p. too much auxin is passed by the bridges to maintain the high auxin levels need to If I try this again on my sango, generate roots. There was
a thread a couple of years ago that discussed ground layering with vertical cuts and IBA in PEG. I tried vertical cuts painted with 3kppm IBA + 1250ppm NAA in PEG40 on a.p. "Higasayama", a.p. " Nishiki" and an acer shirawawanum. The cuts simply healed shut. I even remade the vertical cuts and repainted them in mid-season and they did nothing but 'heal' the cuts. Meanwhile I did produce a successful layer of the very same shirasawanum with a standard complete girdle. Try windows, if you like - I predict failure. Nevertheless, I am trying this on my nemesis a.p. "Higasayama".
I love troubleshooting these kinds of things!
Birds of a feather.
