moreover, why even hypothesize a meticulous zero-sapwood contact scenario if you are adamant about severed sapwood not being able to channel sap upwards?
i mean, if you really think it is an “absolute” then the above scenario you brought up is not really different from a regular graft where sapwood-to-sapwood contact occurs
I think blocking sapwood or not makes no difference. Since the sapwood once cut, can no longer fulfil it’s function of being a vascular connection.
I would not expect a difference in vigor. Except from maybe the graft with blockage between the sapwood to heal a little slower, since it has a larger “gap” to bridge with callous around the blockage. That is if the blockage is a thick piece. If just a drop of wood glue is enough blockage in your mind. I don’t think there will be any difference.
Becuase i tried to suggest a non biased experiment. If i where to design the experiment assuming i was right, it would be bad science.
I tried to propose an experiment that would find out “how it works” and not one to just proof “I’m right”
Yes, i think it’s no different from a regular graft. You however think otherwise. So to convince you. I have to disprove it. And blocking the sapwood and have a graft be no different seems like a good experiment for that.
where would the sap come from or go to, if the sapwood is totally blocked? i don’t follow your argument here. Could you explain further?
i do however think this is going off topic enough. If we go any further and actually go and do my suggested experiments. I think it’s time to make a separate topic for that.
ok i now see what you are saying, and please correct me if am wrong interpreting your assertions: you are saying that once xylem is cut, that there will be no upward flow whatsoever, and that sapflow will only commence with cambium contact?
you are literally saying cambium contact is the only thing that will provide moisture and nutrients to the scionwood?
is this correct?
btw, as for my argument, what i was trying to say was that xylem flow resumes between old scion xylem and old rootstock sapwood if they are abutting each other, and need not wait for new xylem to be produced from cambium. To me, upward flow will be compromised due to impeding factors i mentioned in my earlier posts, but it does not go down to zero.
by reading your posts it seems like you are saying that xylem vessels are a solid-state entity. An all-or-nothing system that when severed, it loses its function outright(at the junction of scion and rootstock), is this what you meant?
figured i’d search my ancient usb drives for photo documentation while waiting to be re-engaged.
found below which should be visible evidence of active upward sap flow. Sap is denser than water, so takes more effort to push it upwards. Not only is it subject to gravitational pull, but also subject to intrinsic vascular resistance, and 760 mmHg of atmosperic pressure bearing down on the exposed xylems. The upwelling of white sap latex forming blobs of fluid against gravity not only indicates substantial positive pressure, but obviously indicates flow of sap continues upwards. No need to wait for cambium to produce new xylem vessels which would take time to differentiate. Also evident the xylem vessels of this would-be rootstock has not been totally blocked since it continues to pump fluids against gravity. Thus said, many of what once were the contiguous xylem vessels of the stems cut from this would-be rootstock wont be any different and will still be able channel fluids upwards since xylem is nothing more than a static porous bunch of conduit pipes.
intended scionwood will benefit from this voluminous upward flow compared to a weaker upward flow resulting from intentional blockage with foil/wax at the interface of scion xylem and rootstock xylem. In
fluid physics, resistance is inversely related to pipe diameter, so even with the same pressure pushing up the sap, intentional blockage at xylem/sapwood junction will limit sap flow just to the periphery and against higher resistance, so this compromises the scion.
hopefully this enough proof of what was pointing out, as it sounded like was doing any would-be grafter a blatant disservice when said optimizing xylem flow is at least as important as cambium approximation. I also feel that any sap flow from roots to scion at the time of grafting is at least as important as having to wait for cambium to reconnect, because if that concept is the only thing to rely on, one will have to wait for new xylem to be fully differentiated before actual root-to-scion flow is initiated.
I had posted this picture in a persimmon grafting thread, but this was also a suggested home for it. It’s the graft union of a non-astringent kaki on top with an astringent seedling rootstock. I thought it was interesting to see what’s going on inside a graft.
The fact the pruning cuts can bleed sap, is not proof that xylem once separated reconnects.
The phloem usually differentiates before the xylem. And that would be the first access the scion has to resources after grafting.
if you look at this topic. From the 3e picture onwards.
You can clearly see where the stock and scion where grafted. And you can clearly see that the xylem did not reconnect. And the rootstock blocked the severed xylem, visible from the discolored lines. Just like you see when the tree is trying to block of a fungus growing into the wood.
This might not be hard evidence (you’d need a controlled experiment for that) but it at least makes it likely that grafts with bad xylem contact do just fine.
Always go for good cambium contact over good xylem contact. All sources on grafting if ever seen emphasize cambium contact is most important during grafting.
it will never reconnect @oscar, we are actually in agreement on that one, since dead material cannot organize. What we don’t agree on is that you claim that sapwood can no longer channel sap upwards once cut. Fully differentiated xylem(sapwood) is nothing more than a static bunch of pipes with holes subject to pressure buildup upwelling from the rootstock.
upwelling of sap as i documented on my recent post-- forming blobs on top of those stems, and against gravity/atmospheric pressure should be enough proof that xylem or sapwood does not lose its channeling properties(at least not all of it, if reattached quickly enough with minimal exposure to air and minimal debris/sap-gumming)
i also don’t disagree with what everybody says that cambium contact is important during grafting, but what have to point out that xylem sapflow is at least as important, and more urgent than cambium reconnecting right away.
anyway, will try to do it in most simplistic but reasonably tangible thought experiment: if we were to go back to the severed stems on my recent post depicting active upward flow of sap, please tell me your thoughts on the following.
say, if we hypothetically envision below scenarios:
i think that #3 will wither die quickly, while #2 will last longer than #3, while #1 will last the longest of them all, being fed with nutrient-rich sap and not just water. Would you at least agree with me on this one? Please tell me your thoughts.
i forgot to add a most salient point @Oscar… For many fruit trees, it takes months after grafting before functional sapwood differentiates from the adjoined cambium layers. If i remember it right, apples can take 90 to 120 days before actual sapflow from “new” xylem starts flowing. If there was zero sapflow before then, where will the scion obtain moisture and nutrients from?
as i see it, a recently-grafted apple scion would be no different from #3 of the scenarios i posted above. No stem could last 3 months under full sun, let alone expect it to grow several inches within 3 months of grafting with zero sapflow
I think we should be clear that the scientific and professional consensus is that cambium contact is most important during grafting.
Your opinion that xylem contact is as important or even more important. Is something i strongly disagree with.
And i think it’s bad advise to give people new to grafting.
It’s an interesting theory. But as far as i can tell unproven. And in my opinion unlikely.
Upwelling of sap (bleeding) from a cut, is not the same as a scion being able to absorb and transport that sap upwards trough severed xylem.
Also notice how bleeding of cuts is usually a short term thing. A few minutes to hours and the cut has been sealed off. Even if you paint over the cut. (seal off from air)
If you where to graft a dormant non bleeding scion. To a bleeding wound of a rootstock. The scion (cut at the top) would not bleed.
Also notice how for fruit tree’s the rootstocks usually don’t bleed when grafting in the dormant season…
Where do you get your information from? I’ve seen a lot of speculation from your side, without a source. Making claims that go against current scientific sources.
The things I’m saying are in agreement with previously posted scientific sources in this topic like:
https://www.frontiersin.org/articles/10.3389/fpls.2020.590847/full#B143)
For grafting to be successful, a number of complex biochemical and structural processes are involved. The latter result in establishing a connection between the root-stock and scion. Adhesion of parenchyma is the first step for union formation followed by formation of vascular elements and their differentiation into xylem and phloem. Formation of vascular connection between the stock and scion during wound healing is of utmost importance as the wound given to the stock and scion during grafting causes disruption of the vascular system in plants (Asahina and Satoh, 2015), hence connecting up of the vascular system is required to facilitate water uptake as well as to ensure nutrient transport to the graft junction. In addition to this, vascular reconstruction enables macromolecules to be transported across the graft union (Harada, 2010). This specifies that vascular differentiation is imperative for grafting success during the process of wound healing. Five histological stages are reported to come about during graft union formation in rootstock scion combinations: (1) formation and orientation of necrotic layers, (2) callus cell proliferation, (3) formation of callus bridge at the graft interface, (4) vascular cambium formation and (5) vascular tissue reconstruction between the stock and scion (Figure 3). Except for the outer cortex necrotic layers tend to disappear by the cellular activities in the callus. In most of the cases the portion of necrotic layers in the outer cortex gets transformed into bark (Yildirim et al., 2010). The process of graft union formation is temporally separated.
A simple way to prove it would be to,
strip both rootstock and scion of bark/cambium for say 2 inches each. And than graft with just the xylem (sapwood) alone. And wrap that sapwood. And see if it survives. My bet is it won’t survive.
Also think about technique’s like T budding. You completely remove the xylem (wood) from the T-bud when budding. And you don’t separate the xylem on the stock. There is no xylem connection there. And still the graft works great.
do you have a source for this?
And aren’t you forgetting the phloem?
Our results point to a scenario in which attachment occurs first, followed by phloem reconnection at about 3 DAG, root growth at approximately 5 DAG, and xylem reconnection at around 7 DAG.
They showed that a phloem connection (moving fluorescent molecules from the scion to the root) occurs before a xylem connection. (moving fluorescent molecules from the roots to the scion)
So for 6-7 days there was no transport up from the rootstock to the scion. While there was transport down from a phloem connection after just 3 days.
I think this alone disproves your theory.
To characterize further vascular formation and cell differentiation at the graft junction, we visualized xylem by clearing the tissue using a previously described method [35]. New xylem vessels formed above the graft junction 4–5 DAG, whereas new xylem formed below the graft junction 5–6 DAG (Figures 2A and 2B). Since xylem is composed of dead cells, it appears that xylem precursor cells differentiated and underwent programmed cell death to form new xylem vessels. Even in grafts where the old xylem vessels appeared aligned, the new xylem often took an indirect route to reconnect below the cut site (Figure 2A), possibly avoiding damaged xylem elements.
This clearly shows severed xylem is not reconnecting, even if aligned.
The newly produced xylem, from programmed cell death of xylem precursus grown from the new cambium connection. Becomes the xylem connection after grafting.
i thought i already proved that sapflow does not stop when xylem is cut and continues to get pumped upwards against gravity. Please tell me what you think regarding scenarios i posted. Would you rather dip the scion in upwelling sap? Would you rather dip the scion in a vase of water? Or would you rather keep the scion totally deprived of sap for several months?
Your assertion that sapflow stops immediately is what i thought was wrong. The photographs i posted weren’t enough proof for you?
i disagree, it will not be totally sealed off, and will continue to flow upwards(albeit compromised by factors i mentioned previously) especially if the seal is air-tight and the scion is adjoined to the rootstock in timely manner with minimal exposure to air. If sapwood flow was to be reduced to zero, then not sure how a well-adjoined graft can leaf out, grow several inches of upright stems, or even produce fruits within 3 months. That won’t happen in scenario #2 i posted, since water is just hydration and zero nutrients. And definitely won’t happen if the scion’s basal stem was to be sealed with air-tight wax and leave the scion to its own devices and under full sun.
no it does not @Oscar . If remember it right, that only applies to herbaceous species, for woody dicots, especially woody conventional fruits it takes months for actual reconnection of vascular tissue to occur
i do have a source for this and will post it when i find it.
no, phloem will have nothing to do with scion’s development(at least initially while rootstock has enough stored food from previous growing seasons while phloem was feeding it). Not sure if you’ve seen some posts here, but girdling is supposedly performed to severe phloem flow in order for the scion be more productive with sweeter fruit, since all photosynthates are locked up in the scion wood.
ok, @oscar , finally found it. The species you mentioned on that reference is Arabidopsis, which is a herbaceous dicot. It takes months for “new” xylem to be functional in grafts of woody dicots. An apple scion can;t possibly be producing regular sized foliage/blossoming/bearing fruit if it was to wait 4 months for xylem to channel sap from rootstock. Where do you think the scions will be getting sap from?
also just realized @oscar, my reference is the same as yours!
anyway, you missed reading that part which i highlighted above regarding the time it takes for apple scions’ de novo xylem production
How would T-budding work than? All your arguments state that there must be a xylem connectio at time of grafting for the graft to survive. But when T-budding you remove all the xylem from the bud.
You seem to be literally cherry picking information that suits your theory.
The source you referenced. (is about cherry’s)
It goes into how the different hormone concentrations on the different sides of the graft union. Affect healing. How the differentiation of xylem and phloem happens. etc.
Literally the first part of the paper (after the summery) is
Successful graft unions result when cells at the surface of both scion (stem) and rootstock (root) tissue complete the sequence of wound response (callus proliferation and differentiation), to creation of a continuous cambium and vascular system between scion and rootstock.
actually feel it is the other way around. You were skeptical about my post about apple scions when i mentioned apples take 4 months to produce functional xylem. You asked for the reference regarding my claim, and lo and behold, it was the same reference that you posted which you apparently did not read in its entirety. Instead you posted how quickly xylem reconnection takes for a herbaceous species that isn’t even in the same family or order to which apples belong to. Yes, it is 7 days for Arabidopsis herb @oscar, but please please just read further down the reference that you(and i)posted, as that mentions it takes 120 days before definitive new xylem connection is produced in apples. Already posted and highlighted a screenshot of the page of your reference indicating just that.
Again i ask-- and this bears repeating-- from where will the nodes of such apple scions get their sap from if it takes 4 months for definitive xylem reconnection to occur? You insist that sapwood flow stops entirely once sapwood is severed, and have to wait for new xylem to reconnect. Can you please engage me on this one?
it is not about cherries, please read the entire reference you and i posted.
t-budding is a totally different scenario from the same-caliper stem graft scenario i mentioned . When you t-bud, you implant a tiny piece of living tissue. The smaller the tissue, the less sap flow it needs. All dormant buds start that way where the cambium of the bud doesn’t need functional xylem yet, since there is no need for it(other than its base abutting the sapwood of the trunk/stem from which it derives sap from). In hydraulic physics, resistance is directly related to the distance which the fluid needs to travel. There is not much resistance if the tiny clump of dormant cells are literally sitting on sapwood. It will only need fully functional ‘de novo’ xylem when it starts leafing out and developing stems of their own.
but when you graft stem to stem, where there is some distance involved to reach the node/s and compromised status of sapwood, a constant flow from sapwood(albeit hindered) is vital to sustain such nodes.
no stem will survive 4 months without sapwood flow
i don’t think there is any way to change your mind. So I’m out of this conversation. It was fun for a while. Thanks.
on a last note, all scientific sources (and professional literature) i have seen. claim cambium contact leading to callous and then differentiation into vascular elements (like xylem and phloem) to be the mechanism behind grafting.
You’re going directly against this, making wild claims without any backing them up with scientific literature. All your links to literature are to related issues. But your core claim is all speculation. You seem to want a way higher degree of proof from me, than you hold yourself to.
For T-Budding. I’ve seen T-buds grow a foot (or several) within a few months from grafting. I hardly believe this is possible without a vascular connection. And it is well documented that there is a vascular connection way sooner than months from grafting.
This is also seen in the timeframe source you mention. It’s about when there is no more callous tissue formation, and the last callous differentiation has happend. And the grafting/wound healing response is completely finalized. But long before than, the first vascular connection has happend.
there are also plenty of example of multiple plants where you can brake a shoot. but leave a little bit of bark (with cambium and vascular elements) attached. And the shoot will survive (and continue to grow)
While thus having completely severed the sapwood. It does grow slower though.
that is ok @oscar, don;t feel obliged. I am actually obliged to post a disclaimer for anyone reading this that my posts are nothing more than applying(my personal)logic to what scientific reference points out.
i see that you are applying your individualized logic too re: your personal experience and observations, and that is great. It is why we are in discussion.
have seen that too, but t-buds are totally different because the node tissue(of the scion) are literally sitting on old sapwood that has not been compromised(not been cut). So they grow pretty similar to how dormant nodes would grow. Same-caliper stem graftings don’t have that luxury. Sapwood flow is at its most optimal with t-buds.
i agree that it will grow slower, but not sure about your claim about completely severing the vascular elements(i presume you pertain to xylem elements being totally severed), because if that was the case then you are implying that a piece of bark and the ~two-cell thick cambium(flapping in the breeze) and a sheath of phloem would survive. You need a microscope for that.
i guess now is my time to ask you for your source on this, considering that the reference you(and i) posted indicate it takes months for new xylem to be reconnected in woody trees. Apples, specifically.
you say it is well documented. If well-documented, did it indicate how many days an apple scion produces fully functional xylem? Not months? If not apples, what fruit species were elaborated on? Were they at least of the woody type?
Please post your reference on this before you leave this conversation, as it is a plausible explanation for your assertions. It will also be a bit of a game-changer considering the claim runs counter to the previous literature you and i posted earlier.
that is your point of view, and that is ok. I do think the same of your claim that sapwood flow stops altogether once cut, and that no sapflow resumes even when adjoined by grafting. Can you please post your scientific literature on this before your leave?
