the cambium is always next to the sapwood (xylem). Thus if you can peel of the bark (bark is slipping) where your peeling, that’s where the cambium is.
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This is where i disagree.
Sapwood contact will do nothing. There will be no sapflow once the xylem has been severed.
The new cambium contact will form first, then you’ll get new phloem contact a few days later. And a few days after that you’ll get newly formed xylem forming the final “bridge” and making the graft complete.
In your elm tree example. The xylem/sapwood has not been severed. And thus it’s completely different from a graft.
If the xylem is severed it exactly means there is no more sapflow in the xylem. And thus no more sap flow between scion and rootstock.
The first new sapflow that can happen is after the callous tissue’s touch and the first new phloem has formed. After that new xylem will form, and than you have restored all the severed connections.
Before the new phloem has formed after the cambium callous has connected, there is no contact between scion and rootstock. The scion is surviving on stored resources and moisture. That’s why it helps so much to avoid the scion loosing moisture.
Nope. As soon as the cells have differentiated to xylem, it starts fulfilling it’s function. It does not have to die first.
Think of it this way. If you where to do a graft. Where you replaced a little piece of the sapwood with something to block it. (bit of wax?) but have the bark (including cambium) bridge that blockade. Would you expect the graft to survive long term?
And what about if you did a graft without the bark/cambium. only connecting xylem/sapwood and than wrapping it. Do you expect that graft to survive for more than a few months? (might survive a little while on stored moisture and resources)
If your correct. that graft without cambium would survive as long as there is a branch below the graft “feeding” the roots to keep the roots alive.
If I’m correct, the graft will die within months.
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while we both agree that xylem is dead material, the difference between our discussion is that you think xylem won’t channel sap upwards if totally severed and then re-attached. I actually think it will continue to do so and that it is in fact crucial to survival of the scionwood more than anything else.
it may still survive since sap literally upwells, and will flow upwards (but only peripheraly, since the sapwood has been blocked) into scion cambium since there will be contact, but i actually think it won’t be as vigorous in growth compared to a scion that has a high surface area of sapwood snugly in contact with each other.
should have mentioned this earlier, but have already done this a long time ago, and proven it to work.
as long as you seal the wound/junction air-tight(wrapping with something that is durable/does not decompose), it will work. I even have soft findings indicating the girdled scion to be more fruitful on its frist or second years compared to grafts where cambiums are well-approimated , since the scions are hogging all their products of photosynthesis and won’t have to share with the roots. If you try it, you;d also notice that the scion will get thicker in girth compared to the rootstock, especially if you decapitate the rootstock, graft the girdled scion, and not allow the rootstock to activate nodes to leaf out from below the graft
lastly, xylem attains full functional status when it has fully differentiated(fully dead, that is), and not fully funtional while it is still alive.
but it, too, just like most biological conduits, will attain a peak, and then regress. It is atherosclerosis in humans, and full lignification into heartwood in plants. The reason why trees live long is that they continue to produce sapwood, with humans we are only assigned one aorta, and this aorta and all its branches get gunky at some point
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Really think you guys should break this out on a seperate thread because it’s very technical Agronomy | Free Full-Text | Nitrate Transport Rate in the Xylem of Tomato Plants Grafted onto a Vigorous Rootstock | HTML
ui_ep_26640.pdf (5.5 MB)
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And apparently theoretical, since I don’t see what research this comes from as far as exactly how grafts heal. It also doesn’t seem instructional. The main instruction I have seen time and again from experienced grafters and in literature I’ve read is, try to establish as much cambium contact between scion and tree wood as possible.
How is the nature of the xylem of practical consequence in this exercise?
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We know that " in grafting, as well as budding, the vascular cambium of the scion or bud must be aligned with the vascular cambium of rootstock. In woody plants the cambium is a very thin ribbon of actively dividing cells located just below the bark. The cambium produces conductive tissue for the actively growing plant (Figure 1). This vascular cambium initiates callus tissue at the graft and bud unions in addition to stimulating tissue growth on the basal ends of many vegetative cuttings before they have rooted." Grafting and Budding Nursery Crop Plants | NC State Extension Publications . That’s why as I mentioned I think transportation is a better subject to be broken out into a different thread and not part of cambium though I see the relationship. As one study says " The xylem in fruit of a number of species becomes dysfunctional as the fruit develops, resulting in a reduction of xylem inflow to the fruit. Such a reduction may have consequential effects on the mineral balance of the fruit. The aim of this study was to elucidate the dynamics and nature of xylem failure in developing apples (Malus domestica ) showing differing susceptibilities to bitter pit, a calcium‐related disorder." That’s clearly not a discussion on grafting or cambium Causes and Effects of Changes in Xylem Functionality in Apple Fruit . I’ve implied the need for discussion many times with threads like this Pear Rootstock influence on pears fruit size, tree growth, nutrition, longevity etc and this Pear rootstocks influence on Fruit size. It’s my belief as an example ohxf333 has smaller fruit for years after planting it that are inferior to other fruit. That’s just it its a belief. Have seen no studies to support that as its based on observation and has nothing to do with cambium contact, color, or callusing. For those wanting to know more on the hypothesis and observations on this subject that’s not about cambium see this sap | plant physiology | Britannica
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It requires a certain amount of well lit leaves feeding each piece of fruit to have a high quality harvest, so perhaps the problem with 333 with trees you have is that the ratio of leaves to fruit is not adequate. A lack of vegetative vigor becomes a problem when fruit is not well supplied with sugars from the leaves- as you know.
What makes moderate vigor desirable is that growth is adequate to feed fruit without extending so far it shades the leaves feeding the fruit.
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oops, sorry didn;t mean to hijack the thread as i admittedly tend to ramble.
ok, am guilty as charged, as the majority of stuff i post here is nothing more than personal/practical experience or personal experiments and analyses. Admittedly tend to exhaust all possible permutations and rationales that aren’t published by mainstream academia so have to make that public disclaimer. Was merely trying to convey a bit of optimism when it comes to would-be grafters who might fret about not getting good cambium contact due to scion-rootstock dimensional differences-- that there is a fighting chance if sapwood contact is quite snug with minimal air gaps in between.
it is actually great advice, since it speeds up sealing off open wounds, especially in an area where paraffin film and plastic wrap degrade pretty quickly. It also helps speed up a cylindrical connection of the stem perimeter when xylem connects, strengthening the graft.
again i agree that aligning cambium makes for a great graft, but there’s not much else mentioned by the general consensus, so wouldn’t be much instructional if another poster reiterates it and not consider other variables that could optimize or compromise a would-be graft
anyway, not sure if the following may be instructional or maybe something new which academia haven’t yet published about grafting:
- the speed by which the grafter processes the rootstock and scionwood help minimize coagulation of sap due to ambient exposure. The tendency is get preoccupied whittling the scions and rootstock about cambium contact, but several minutes of approximating can be detrimental.
- grafting during windy weather won’t be as optimal as it accelerates desiccation of sap and inadvertent dusting with airborne debris on the surfaces of scion and rootstock which will occlude xylem flow
- that when grafting stems with dimensional differences, it is not exactly a lost cause if the graft union don’t make perfect cambium alignment, as long as it is sealed air-tight with durable wrap and that the scion wood is tightly abutting the rootstock. Too much air getting into graft junction won’t be good, apart from being an access point for microbes/spores to settle and proliferate, considering that xylem flow during grafting season is rather nutrient rich and sugary
- watering the rootstock at least a day before grafting would help optimize sapflow
admittedly rambling gibberish again(with no literature to back me up) but merely trying to be optimistic while also diversify grafting advice, and hoping some might be worthy of consideration 
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Thought your post was very good I like all types of perspectives and ideas. Didn’t want to get @Olpea thread to far off topic. What you posted we could spend a lot of time discussing on another thread. I’m glad you all bring this stuff up. Your all making me think about things I’ve not considered in years.
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Thanks @clarkinks and i do apologize to @Olpea for my exuberant posts. Reading through the posts, i felt that the question was already answered so ended up digressing to other topics which thought might be relevant, considering that the post is amost 7 years old and dormant since
Ok, enough of my excuses…
So going back to topic, it is impossible to pinpoint exactly where the cambium layer might be with just the naked eye, being such a thin film of undifferentiated cells. And as for the color–as with most types of cells, be it plant or animal, undifferentiated/primordial cells tend to have the least pigmentation.
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If posted sources up higher in the topic.
https://organismalbio.biosci.gatech.edu/growth-and-reproduction/plant-development-ii-primary-and-secondary-growth/
And the link Clarkinks posted,
Goes into more detail. (including times measured from moment of grafting to different healing stages and differentiation stages)
I agree with you there. The cambial contact is important. This is reflected by my own experience and all literature if read.
It is not. That’s exactly what i am claiming.
jujubemulberry however is claiming xylem (sapwood) contact to be more important than cambial contact.
If tried to disprove this in my eyes false claim. That i think is steering (would be) grafters in the wrong direction, practically.
Are the points i disagree with, and tried to argue against or disprove.
My apologies jujubemulberry if i quoted those points out of context. Id recommend everyone to read them in the full post and context.
I think if made my counter argument against the sapwood contact being more important than cambial contact in grafting point. So i won’t go more off topic.
Back on topic.
i agree with jujubemulberry that you probably can’t see the cambium itself with the naked eye.
We “aim” for the “green line” (or i aim for the spot where sapwood connects to the bark, basically where the bark would peel off)
Since the cambium is right next to it, and so thin that we can hardly see it.
The line isn’t always green by the way, have you ever looked at B9 rootstock while grafting? It’s a nice pink/red
I think the cambium itself is mostly translucent or lacks a specific colour.
But when it differentiates it gets a visible colour. mainly in the direction of the phloem. (green, or red/pink in case of B9) The part that becomes the xylem gets a woody white colour.
this is relevant, because the question in this topic was. Not only what colour the cambium was. But also where it was or how you would find/see it.
I think the cambium lacks a clear colour. And it is so thin that you won’t reliably see it with your naked eye. And you can easily find it, by looking for the contact area between the white wood (xylem), and the coloured line in the bark (phloem). Between those, is where the cambium is at.
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well i should apologie to you too @oscar . I hope i didn’t come off as dismissive. Anyway, was merely diversifying possibilities and permutations not mentioned in literature since all literature already recommend approximation of cambium layers. Just like you and everyone else in this forum, i aim to approximate cambia(or so i think am capable–the tiny film of cells that cambium is). So my simplistic and humble way of putting it is: if the scion is not the exact shape(cross-sectionally) as the rootstock stem, and often it is not, then i just strive to make sure their sapwood are snugly abutting each other, at least to maximize upward welling of sap.
If you have proof of this, i would love to see it
But i understand if you don’t have. I can’t keep track of how often i did something out of curiosity and forgot to photograph/document it.
luckily with how good camera’s are on phones, it’s getting easier and easier. I’m trying to get into the habit of just excessively photographing experiments. That is, when i still don’t forget.
grafting/gardening can be quite like meditation. Clearing your mind of all other things than the thing your focusing on
i see no reason why you should apologise!
we where talking about growing fruit and grafting on a fruit growing and grafting forum. That’s what it’s here for.
Anyway, if enjoyed our discussion. And hope you have to.
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yes, will do it again this spring. I did it on citrus , but will do it on jujubes since its what i have a lot of currently
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Raf,
That’s a kind sentiment, but absolutely no apology necessary. Of course just because I started the thread doesn’t mean I own it. I think the topic has wandered in interesting territory by yours and others insights and thoughts. A forum topic is a conversation, which can and do, drift in many directions, which can make it all the more interesting.
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so @Oscar, now that @Olpea has given us go-signal to digress, i forgot to ask you what your thoughts were on the hypothetical scenario you brought up. I actually think the above scenario will survive due to peripheral upflow of sap despite the sapwood being totally blocked off with wax, but it won’t be as vigorous as a graft where the sapwood is not blocked.
would you think the same or do you suppose a regular graft(with no sapwood blockage) will be no more(or no less) as vigorous as the no-contact sapwood scenario you brought up?
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.