I’m very interested in this discussion because while I have propagated by many means, I have not yet had any success grafting. What is the easiest species or plant to try on for beginners to be successful?
In that sense xylem is just the wood. This surprised me because I knew xlyem transported water/nutrients from roots to foliage, but I thought this occurred only on the outside bark. This makes sense to me (in one sense) because I’ve seen trees completely hollowed out by rot, but still alive, with just a really thick layer of bark. However, in that case, there must be just enough xylem tissue in the thick bark to transport water/nutrients back up the tree.
A few years ago I completely girdled a couple elm trees (to kill them) but I was surprised they made it through two summers before they died. Upon reflection, this would seem to confirm the xylem is in the wood itself, else how would the tree remain alive for two summers?
Referring back to the illustration I linked above and applying it to Matt’s pic of the open bud flaps, the vascular cambium is indeed what Fruitnut refers to. It’s more or less invisible (or indistinguishable) from the xylem (blond wood on the little trunk) and the blond colored phloem on the inside of the bark flaps. It would make sense it’s “invisible” if it’s only a couple cells thick, as fruitnut suggests.
So the order from outside to inside seems to be: cork bark (we all know that is brown), cork cambium (maybe that’s the green stuff, but that’s not the type of cambium which concerns grafters), blond colored phloem (fairly thick layer), invisible vascular cambium (for grafters, this is where the “pay dirt” is, even though the pay dirt is extremely thin), the xylem (which is basically the wood-the “sap wood” in illustration Tony provided). Lastly is the heart wood (which is the very core of the tree and probably it’s only function is structural strength).
Thanks for all the responses. If I have this right, I’ve definitely learned something. Either way, the cambium which concerns grafters is not green, nor is it a dark line (but it can be just “inside” the green on brand new shoots, i.e. current season growth). I bet I’ve read a hundred times the cambium is green (and repeated it some myself) which is incorrect. I find that somewhat amazing. That is, that the general consensus of even trusted publications can be incorrect on something which should be a fairly straightforward anatomy question.
All one needs to know to graft or bud is where the cambium is located. That’s the part that separates when the bark peels off wood.
One other thing I’d point out in post 9 above of Matt’s second picture down. The cambium would be only in a very thin strip around the small elliptical area of whitish wood in the center of that bud. All the light green material outside the elliptical area of wood is probably bark. The bark won’t heal to wood of stock. Graft will likely succeed esp on apple but is cut a little too thin to include much cambium layer, IMO.
Well, this is a very useful thread. I’ve always wondered about this issue and now I think we have the answer.
But it does make me wonder just how thick (not very!) those two cells of cambium make the layer which has now been identified as a grafter’s pay dirt. Would you have to use a microscope to see the individual cells, or would a good jeweler’s loupe do it? I imagine somebody knows how to stain the cells to make them stand out better. That would be interesting, and might even be useful in practice.
The cambium layer changes very rapidly. Cut off the water and those cells quit dividing. Then the bark won’t slip and you can’t T bud. Water heavily and in 7-10 days the cambium is dividing rapidly, bark slips, and T budding is on.
Olpea, some of the wood is xylem, but as the tree grows the interior xylem dies and becomes heartwood with very few living cells (the living cells are like the fungus police). The older the tree the lower the percentage of the wood is xylem (sapwood).
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.
while it is true that cambium contact is beneficial when grafting, contact of rootstock xylem to scion xylem is at least as vital, especially during spring when net nutrient flow is temporarily in reverse direction(from rootstock to scion–think maple syrup). And of course, at least as important is supply of moisture, which is a perpetual year-round thing from rootstock to scions.
girdling trees actually trivializes “the urgent need for immediate cambium contact”, as the rootstock will actually continue to support all stems/grafts above the girdle, and in fact, all stems/grafts above the girdle will fatten up as the downward flow of sugars and proteins has been permanently severed(phloem).
once the food depots within the roots have been consumed, the rootstock dies first, and only then will the above-the-girdle stems die. Thus said, if scions fail outright on the year of grafting it is mainly because upward sapflow was compromised or lacking, and not because of poor cambium contact, as it is obvious from the girdled elm scenario that zero cambium contact does not kill above-the-girdle stems or grafts.
so going back to the girdled elm trees which were never allowed to have cambiums re-connect: the stems above the girdle were ok, and in fact selfishly accumulating all the nutrients produced via photosynthesis for two years. Meanwhile, the roots were slowly dying of starvation which took two years to consume their unreplenished food depot.
perhaps important to note that roots and stems keep their food depot of sugars mainly in condensed starch form(apart from wood cellulose). My personal analysis on this(maybe am wrong on this one, as haven;t come across literature that mentions this-- but also haven’t come across one that says otherwise)is that come spring, this stored starch is hydrolyzed into simple sugars(which nodes/buds need as food to leaf out), and these sugars in solution exert stronger osmotic/hygroscopic properties than regular starch* or wood, sucking in moisture from the soil, and resulting in an increase in internal volume of fluids. This increase in volume is likely one of main reasons why sweet-sugary maple sap flows upwards.
*if you enjoy baking, then very much aware that cake is mainly starch(which is a complex chain of sugars). And if you want your cake moist for longer periods you have to load it with simple sugars, say, sucrose and/or fructose, as simple sugars have a higher affinity for ambient humidity than starch
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.
When grafting the “pay dirt” is the lateral meristem. This is the layer of “stem” cells that divide. These stems cells then differentiate into different vascular systems (xylem towards the inside of the stem. containing upwards flow from the roots) and phloem towards the bark (outside of stem) the phloem transports both up and down, and can be seen more as a redistribution system of tree resources (sugars hormones etc) but is also responsible for delivering resources to the roots of the tree. The phloem is a more “active” (“pumping” in directions) system. where the xylem is more passive (relying on pressure from the roots and negative pressure from evaporation in the leaves.
Think of the xylem as long continuous straws. (mostly dead tissue)
With flow only going upwards
And the phloem as “tubes” connected to pumps. With flow going both ways. (even adjacent “tubes” can flow in different directions)
The lateral meristem (grafters “pay dirt”) is located in the vascular cambium.
There is however not a super clear line between the lateral meristem and the phloem/xylem. Since the cells from the meristem are in different phases of differentiation to the phloem and xylem.
Anyway the important thing for grafting is, that you get the lateral meristem of the scion and rootstock close enough. So that the exces undifferentiated cells they will produce when damaged (cut) in the form of callous can touch, and then fuse together. And when fused together can differentiate into vascular tissue and thus make a vascular link between stock and scion.
The closer the meristem of the scion is to the stock, the less gap it has to fill with undifferentiated cells. And thus the faster it fills that gap, and the faster there is a connection to initiate the differentiation of the cells to make a vascular connection.
And a faster connection gives the scion less time to run out of resources (water and nutrients, but mainly water)
Another important factor is to not damage/kill to much of the meristem. Since then there is “dead” debris between the 2 meristems trying to fuse. This happens for example when you cut a scion and than let it dry out before pushing the cut surface to the stock.
Or when you coat the cut parts of your graft with a fatty film. (eating chips and then touching the cut surface? or using a oil covered knife)
Back to the original question of the topic.
I think the cambium itself is to small (few cells thick) to actually see with the naked eye. While grafting we aim for where the meristem cells differentiate into the phloem (the dark (green) line that’s visible) On the inside of that line we find the vascular cambium/lateral meristem. As far as I’m aware the cambium is reasonable translucent. And basically has the colour of the dye it absorbs in microscopic pictures. The cells in the meristem are smaller though. And increase in size when the differentiate/elongate.
It might have a slight tint, but due to it being so thin, a small coating of cambium cells on the xylem for example will likely not give a visual colour change.
i suspect the colour to be different for example on B9 (redder translucent) than on M9. (translucent or green tint)
Anyway the exact colour or spot of the cambium does not matter much. Since it’s so thin you could never match it 100%. You just want to aim for “close enough” and let the callous make the connection.
when grafting, (in chronological order)
we cut/damage the scion and stock. On the cut surface of the lateral meristem, callous tissue (undifferentiated cells) will start to form excessively. Until they have bridged the gap between scion and stock.
Once this happens these cells will start to differentiate into vascular tissue’s.
On the inside (towards the wood) it will form xylem tissue (mostly dead long straws that only transport upwards)
On the outside (towards the bark) it will form phloem tissue (living, actively “pumping” cells, and support cells) that translocate resources (transport both ways, up and down)
only the newly formed xylem will transport upwards over the graft union. The old cut xylem no longer does anything.
disclaimer and sources
In the above text you should read secondary xylem everywhere if written xylem. I left out the secondary everywhere to avoid confusion. Since the difference between primary and secondary xylem is not relevant here. (for completeness sake. the primary xylem is formed by the apical meristem (the growing tip of a shoot) while the secondary xylem is formed from the lateral meristem’s cells (in the vascular cambium)
see for example the following sources for more info/explanation. (if oversimplified some things)
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!
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
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!
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.
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 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 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.
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.
I don’t know if everyone noticed, but this topic was a resurrected old thread.
Still, some interesting new comments.
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.
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.