Just exactly what color is the cambium anyway?

[clarkinks]

This is a great topic the answer is green. Went through a terribly frustrating process with this years ago when grafting some 6 or more Japanese plums to western sand cherries. The problem was the layer was so thin on 1 or more of the plums I was concerned I would fail at it as there was no room for error. The best way to approach this is by literally breaking every layer and what they do down in detail. This website breaks the layers and their purpose What are the Layers of a Tree Trunk? | Complete Tree Care
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What are the Layers of a Tree Trunk?

Posted on [July 12, 2019]

One of the most interesting facts about tree trunks is that they have 5 different layers! Continue reading to learn more about these 5 tree trunk layer, including what they do!

Parts of a Tree Trunk

Tree Trunks

As mentioned, tree trunks have 5 separate layers to them. They are the outer bark, inner bark (phloem), the cambium cell layer, sapwood, and heartwood. Each layer has their very own purpose, but overall, the trunk’s primary job is to protect and support the tree. Look below to review each layer and what they do.

Outer Bark

Like a shield, a trunk’s outer bark is there to protect the tree from its outside surroundings, including inclement weather, wildlife, pests, and more. It also controls moisture, by both preventing excess moisture in the rain and snow, and retaining sufficient moisture levels during dry seasons. It also provides insulation in cold weather and protects against sunburn in the summer.

Phloem (Inner Bark)

The phloem, or inner layer of bark, is where food and nutrients are passed through the tree. This layer has a very important job, but a very short lifespan. It eventually dies, turns to cork, and becomes part of the outer layer of bark!

Cambium Cell Layer

The cambium cell layer is interesting because it is the part of the trunk that grows. Each year, this layer produces more bark and wood as a reaction to the hormones being passed down from the leaves along the food pipeline. These hormones are called auxins, and they are very important because they stimulate new cell growth!

Sapwood

Sapwood is new wood, and serves an important role as the tree’s water pipeline, delivering water to the entire tree. And as new sapwood is created, the inner cells lose their vigor and turn to heartwood.

Heartwood

Heartwood is the most inner part of the trunk. It plays an important role in balance, stability, and security for a tree. Technically, heartwood is dead, but it does not atrophy or decay (unless the outer layers are jeopardized). It is made up of a hollow, needle-like cellulose fibers that are joined together by a glue-like chemical called lignin.

Additional Parts of a Tree Trunk:

The pith is made of soft, spongy parenchyma cells, which serve the purpose of storing and transporting nutrients throughout the tree. The medullary rays are cellular structures found in only some tree species., and appear perpendicular to the growth rings. The growth rings, also known as Dendrochronology, appear one at a time, once per year, darker in the fall and lighter in the spring and summer."

When @fruitnut showed me how to tbud he expressed the importance of leaving the inner wood behind and taking only the outer layers skin wiyh the tissue. We don’t want heartwood or sapwood.

We only want the outside skin of the tree when making tbuds

There was a time when I first began grafting when I felt it was important to peel the vascular cambium from the sapwood and let me say grafts failed 100% of the time. The sapwood needs to go with the cambium in the case of tbudding.

We need to understand how lining up the cambium layers together to encourage callusing works. This website documents the full process of grafting and callusing details more thoroughly broken down than most people will ever care to read. Ive attached it as a pdf should the website be removed later https://www.frontiersin.org/articles/10.3389/fpls.2020.590847/fullfpls-11-590847.pdf (6.0 MB)

[alan]

That makes sense, but how do you know? The cells are not all dead- are you sure the xylem parenchyma don’t play a part in scion survival?

[oscar]

@alan

but how do you know?

To what specifically are you referring?

@alan

The cells are not all dead- are you sure the xylem parenchyma don’t play a part in scion survival?

True, there are living cells in the xylem. they are however not dividing meristem cells. And thus no new xylem connections can be formed inside the cut xylem.

It’s hard to prove a negative. I can’t prove xylem parenchyma cells don’t play a role in grafting success. Just like i can’t prove “invisible ray lazers from aliens” aren’t a factor in grafting success. Although that 2e example being ludicrously overexaggerated ofcourse.

I have grafted small pieces of bark directly to other bark (without xylem in between) and that works. There might have been a few xylem cells though. Or that it works without xylem does not prove xylem has no effect. Again hard to “prove” a negative.

can you prove the “positive though”?
That should be a lot easier.

[oscar]

@clarkinks

https://www.frontiersin.org/articles/10.3389/fpls.2020.590847/fullfpls-11-590847.pdf (6.0 MB)

That PDF is awesome. Thanks for linking it

if i could your post with that PDF more than once i would !

[Olpea]

I don’t know if everyone noticed, but this topic was a resurrected old thread.

Still, some interesting new comments.

@clarkinks

This is a great topic the answer is green.

Clark, I think if you’ll examine all the info on this thread. The cambium can not generally be differentiated by the color green. Looking for a green color will actually mislead new grafters.

I’ve had a lot more experience grafting since I started this thread 7 years ago. You definitely don’t want to try to match up your small chip of a bud with anything green on the rootstock.

@clarkinks

When @fruitnut showed me how to tbud he expressed the importance of leaving the inner wood behind and taking only the outer layers skin wiyh the tissue.

We always remove the heartwood from the t-bud chip. It generally pops right out. Imo, it makes for more successful takes vs. leaving it in like chip budding. Last fall we t-budded about 150 peach rootstocks (two t-buds per rootstock). I think out of all those, we had one rootstock which both buds failed. We get poorer results with chip budding.

[clarkinks]

@Olpea

Technically that’s true but normally it’s green. That was the problem with one of those plums. Exposing the cambium there was no green to be seen or anything resembling cambium. Side grafting it to a Hansen cherry is challenging when I couldnt line it up. I’m referencing this experiment I did 8 years ago "What plum scion wood to use on prunus besseyi ?
clarkinks(5b)
January 25, 2014
What is your opinion of the best plum wood to graft on a western sand cherry? The base is about the size of my wrist. I was planning to use a rind grafting technique. What are your thoughts?
clarkinks(5b)
January 26, 2014 at 10:10AM
Wanted to give a quick update as it may be useful to someone in the future. We decided to use Alderman, Toka, Superior, Kahinta, Waneta, and Gracious scion wood to rind graft over the existing sand cherries because they are hybrids. " garden web since has removed many of those old experiments we did which is unfortunate Compatibility grafting? - #23 by clarkinks

[jujubemulberry]

@oscar

i disagree.

The xylem is no longer actively dividing(it’s mostly dead), and thus once cut can not fuse or merge with other xylem. And thus cannot form a vascular system.

i agree that they will never reconnect as a contiguous entity(being dead material), but what tried to say was that it is important that scion xylem and rootstock xylem be in good contact with no air spaces, no debris, in-between. I mean, cambium contact can wait, but sapwood contact cannot, as evidently, if we envision the girdled elm trees posted by OP, the entire canopy(which we can envision as a hypothetical graft) of the elm tree was alive for two years despite no cambium contact, being supported merely by dead sapwood/xylem. Have to add that just because xylem was severed, it does not mean sap can’t flow upwards between scion and rootstock. what matters is that we max out contact between the two with minimal air gaps/debris so the flow is facilitated.

@oscar

@alan

That would be hard not to accomplish while joining cambiums.

i disagree, it will be virtually impossible to accomplish.
Once xylem (long dead straws inside the woody part of the shoot) are cut. you cannot reconnect them. And connecting them “sideways” has little use.

You connect the cambium. And the cambium grows cells that differentiate into new xylem the old xylem will stay unconnected!

i guess we are a trio in disagreement. Although i partly agree with you both. When we whittle scion wood, especially those with hard sapwood(persimmon, jujube, etc), we tend to make several cuts. And even with one smooth cut, each cut doesn’t necessarily mean it is a planar cut, so the surface will be uneven. Which means there will be air gaps between them. Cutting invoves production of debris, which will result in microscopic blockage obstacles. The act of cutting also involves exposure to air, which result in gumming of sap(think latex), which in turn will be a form of debris that limit contact between scion xylem and rootstock xylem.
i also agree that cambium will differentiate into new xylem, but even though the rootstock xylem is old, it will still be the only source of sap which scion can rely on at the beginning of a graft. New xylem literally has to die first before it becomes functional as sapwood.

[clarkinks]

@oscar

This topic seems straightforward but I think the document I posted is to detailed for this discussion I’m breaking it out into a seperate topic. The document contains details not widely available that apply to grafting Grafting and callusing explained in every detail

[DennisD]

Thanks Olpea in particular for your posting and comment, pointing out that cambium is not always green! My example that illustrates your point involves my experience with top working sweet cherry trees. I began two years ago. At the time all I had researched indicated to me that the cambium layer is always the green layer below the outer bark. So I followed that hint making sure that my scions were in contact with that layer. The bark was easily separating from that green layer so I was convinced it must be cambium. Of course non of my grafts, wedge grafts, t buds or chip buds worked. After they failed the first year, I began to attribute my failure to various factors such as wrong time, wrong season, wrong temperature, but I could not point to a certain reason. Now after reading back thru this thread and all the videos, particularly your posting of the wedge graft, I understand that on my sweet cherry the cambium layer is below the bark cork which and the green layer between the outer bark and the cork is not cambium.
So I hope other’s just starting out to graft have a chance to read your post!
Thanks again to all contributors in this rejuvenated thread for the information you imparted.
Dennis
Kent, wa

[oscar]

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.

[oscar]

@jujubemulberry

I mean, cambium contact can wait, but sapwood contact cannot, as evidently, if we envision the girdled elm trees posted by OP, the entire canopy(which we can envision as a hypothetical graft) of the elm tree was alive for two years despite no cambium contact, being supported merely by dead sapwood/xylem.

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.

@jujubemulberry

Have to add that just because xylem was severed, it does not mean sap can’t flow upwards between scion and rootstock.

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.

@jujubemulberry

The act of cutting also involves exposure to air, which result in gumming of sap(think latex), which in turn will be a form of debris that limit contact between scion xylem and rootstock xylem.
i also agree that cambium will differentiate into new xylem, but even though the rootstock xylem is old, it will still be the only source of sap which scion can rely on at the beginning of a graft.

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.

@jujubemulberry

New xylem literally has to die first before it becomes functional as sapwood.

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.

[jujubemulberry]

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.

@oscar

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?

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.

@oscar

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.

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

[clarkinks]

@jujubemulberry @oscar

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)

[alan]

@clarkinks

because it’s very technical

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?

[clarkinks]

@alan

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

[alan]

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.

[jujubemulberry]

@clarkinks

Really think you guys should break this out on a seperate thread

oops, sorry didn;t mean to hijack the thread as i admittedly tend to ramble.

@alan

apparently theoretical, since I don’t see what research this comes from as far

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.

@alan

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

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.

@alan

It also doesn’t seem instructional.

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

[clarkinks]

@jujubemulberry

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.

[jujubemulberry]

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.

[oscar]

@alan

And apparently theoretical, since I don’t see what research this comes from as far as exactly how grafts heal.

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,

Mechanisms Underlying Graft Union Formation and Rootstock Scion Interaction...

Goes into more detail. (including times measured from moment of grafting to different healing stages and differentiation stages)

@alan

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.

I agree with you there. The cambial contact is important. This is reflected by my own experience and all literature if read.

@alan

How is the nature of the xylem of practical consequence in this exercise?

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.

@jujubemulberry

yeah, really strange that available literature always mention how urgent it is for scion cambium be in immediate contact with rootstock’s cambium, but not sure if any has even mentioned the most critical aspect of grafting–that is for scion sapwood be in direct contact(with minimal air-gaps) with the rootstock’s sapwood.

@jujubemulberry

that it is important that scion xylem and rootstock xylem be in good contact with no air spaces, no debris, in-between. I mean, cambium contact can wait, but sapwood contact cannot

@jujubemulberry

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.

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.