This section began innocently enough as a simple info blog about jujubes. But during the dormant winter periods with no live action to write about, I went back to my roots (ha!) to write more on soil, biochemistry, and soil microbiology in general. I found myself wanting to keep going, and this blog was becoming less and less jujube-specific.
Thus it made sense to restructure everything.
This blog is now The Biosphere Blog, where I will continue writing about these subjects very dear to me.
(And here is my passion project From Soil to Fruit, a combination of the two and very much a work in progress. This is where topics in this blog are arranged in a more structured book-chapter format, to be explored in far more detail.)
Last week was a brief overview of suckers, or shoots that form from adventitious buds on roots. Today I want to pick up from the Sucker Shoot Development section in that post, with more detail and some diagrams to illustrate this development more clearly.
Last week I wrote that the adventitious bud which becomes a sucker shoot arises from the pericycle (picture here). I did that so as not to introduce too many new botanical words at once — it can be overwhelming and headache-inducing, I know!
While technically correct, more accurately, the pericycle actually develops into tissue called the phellogen, also known as cork cambium, and it’s this that the bud arises from. But first let’s back-track a bit before going further.
The previous posts covering root anatomy longitudinally and cross-sectionally focused on the primary growth of a root. Primary growth, in botany, is the growth at a root’s (or stem’s) tip, where cell division and elongation occur.
Secondary growth, in botany, is the growth that causes roots (and stems) to thicken. During this growth, the pericycle forms two types of lateral (side) meristem tissue, the outer cork cambium and the inner vascular cambium. (Fig. 1 below shows this more clearly.) Both of these continue to thicken the root for as long as they keep producing new cells.
The vascular cambium is responsible for the bulk of this thickening. It produces the secondary phloem (food) tissue on its outer side and the secondary xylem (water) transport tissue on the inner side. (What we call ‘wood’ is xylem by the way!)
The cork cambium produces a protective layer called the periderm in botany, but commonly referred to as bark. (’Bark’ is actually the periderm plus the secondary phloem — see Fig. 1 below. Bark includes all the tissue outside the vascular cambium, in other words.) The cork cambium replaces the root epidermis (picture here), which is ruptured by this secondary growth.
The periderm is actually three layers (Fig. 1 below): the outside cork (also called phellum, of mostly mature, dead cells); the middle cork cambium (or phellogen); and the inner phelloderm.
[And yes, the material commonly called ‘cork’ is indeed the cork (phellum) layer of a particular tree, the cork oak Quercus suber.]
Still with me?! Let’s now expand on the Sucker Shoot Development section from last week — this will be so much easier to follow along now you know the above.
Please bear in mind that the following images show only the top half of a longitudinal section of root.
As mentioned earlier, a sucker shoot arises from an adventitious bud in the cork cambium — a bud not originating from stem or root apical (apex) meristem (undifferentiated) tissue.
This bud is nothing more than a small bundle of meristem tissue itself at the beginning, and with no vascular (transport) connection to the root at all. It gradually specialises to form an apical meristem of its own at one end, and vascular tissue at the other.
Primordial leaf tissue then develops from the apical meristem and the vascular tissue develops at the other end to connect with the root’s vascular tissue. (Fig. 2.) Procambium tissue, which will become the primary phloem and xylem of the shoot, also develops and joins with the root cambium.
The bud can now access the mother tree’s food and water resources for future growth and development.
Fig. 3 shows the progress some time later, whereby the bud is larger and more leaf tissue has formed. The vascular cambium has laid down two new rings of wood which enclose the bud’s vascular tissue. Two rings in this case implies two years of growth, but this is purely for illustrative purposes and could be a shorter or longer period.
As the bud’s procambium tissue is joined with the root’s vascular cambium, this enclosure of wood results in the procambium forming a complete cylinder within the bud. This begins to differentiate into protophloem (first-forming phloem) and protoxylem (first-forming xylem).
Fig. 4 shows the final stage of development, with more wood laid down and the bud now an above-ground shoot.
Over time lateral roots will develop on the mother root this sucker is attached to, and it is these roots, and not the mother root, that would sustain a sucker if removed. The detached piece of mother root must contain sufficient number and size of these secondary roots if the sucker is to survive and grow independently as a new tree.
The roots of many plants and trees never see the light of day, and spend their lives pushing ever downwards and sideways in pursuit of moisture and nutrients. The roots of other species however will occasionally send up suckers, or shoots, that grow up and through the soil to develop — if undisturbed — into fully-grown plants with their own root system. The jujube tree is a well-known example of one such species.
Why Do Trees Sucker?
Suckering enables a tree to reproduce itself vegetatively (asexually/by cloning itself) across as much land as its roots can spread. The parent tree may die, but its suckers ensure its genes live on, and often many metres away. (Note that this vegetative reproduction does not apply in the case of grafted trees — here it is the rootstock, genetically different to the tree, that propagates its species by suckering. Rootstock suckers develop into trees of the same species the rootstock originated from.)
Suckering can also be a survival mechanism. The above-ground portion of a suckering species may be destroyed by fire or physically removed, but its below-ground roots usually survive and send up replacement shoots. Disturbing the roots of some species, including jujube, can in fact be a stress signal which increases the amount of suckering.
The World’s Largest and Heaviest Organism is a Suckering Tree!
I had to slip this fascinating factoid in as it’s too good to not share!
‘Pando’ (Latin: I spread out) is a massive colony of identical male quaking aspen trees in Utah, USA, all from one giant subterranean root system. Pando spreads over 43 hectares, weighs about 6 million kilograms (6,000 tonnes), and its root system is believed to be over 80,000 years old (not a typo!).
Having spent the last two weeks underground exploring root anatomy here and here, let’s now follow a suckering root as it produces a shoot en route to the sky. It may help to re-read those two previous posts, as well as refer to these excellent diagrams also previously linked to.
The meristem tissue in plants functions like our own stem cells, in that it is able to differentiate into any other tissue or organ, given the right inputs. Shoot apical (apex) meristem produces all above-ground tissue such as shoots and leaves. Root apical meristem differentiates into specialised root tissues such as the epidermis, cortex, and vascular cylinder/stele.
An adventitious bud, whether on a shoot or root, is one that develops in an unusual place, ie not from the apical meristem. Adventitious buds on shoots help a plant recover from injury, by driving the healing of wounds or the development of replacement branches. Adventitious buds on roots develop into suckers.
Sucker Shoot Development
The adventitious sucker bud arises from the pericycle, which makes it an endogenous structure, one developing from within deep tissue. This contrasts with the more familiar axillary buds found within a leaf and stem intersection, which are exogenous (external, outside).
At this early stage the bud is merely a small bundle of meristem tissue, and without the connection to the vascular (transport) phloem and xylem tissue that exogenous buds have. An apical meristem later forms at one end of the bud, from which young leaf tissue develops. Vascular tissue develops at the other end and connects with the root’s vascular tissue.
The bud may continue to grow over a few years. More leaf tissue forms and wood is laid down during this time, until eventually the bud is a fully-formed shoot which pushes its way through and out of the soil.
Unwanted suckers are best removed when small and young so as to not compete with the mother tree, and with as minimal soil disturbance as possible — mowing or cutting with secateurs at ground level are common methods. Be especially careful when removing any suckers that are very close to the mother tree’s trunk.
Suckers can be severed from the mother root if wanted as separate trees. Dig gently down to where the sucker is attached to the mother root, and sever this on either side of the sucker, making sure there are enough roots on the severed piece to sustain the sucker.
A plant root is an organ, and last week we looked at the specialised regions along a root in a longitudinal (lengthwise) section. Today we go in at right angles and examine what is revealed by a cross-sectional cut across a root.
Before doing so, a very quick up-to-speed on the the classification of flowering plants — of which of course the jujube tree is one — as this is actually relevant!
Flowering plants are the angiosperms (from Ancient Greek: ἀγγεῖον, angeion, case or receptacle, and σπέρμα, sperma, seed — seeds enclosed by a fruit). All flowering plants produce fruits containing seeds, though not all fruits are recognisable as such to the unfamiliar eye. Caraway ’seeds’, for example, are really a dry fruit which contains the real caraway seed.
Angiosperms can be divided into two groups: the monocotyledons (also known as monocots) and the dicotyledons (also known as dicots).
Monocots have a single coteyledon (embryonic, first, leaf), and dicots have two. Monocots have other characteristics such as a fibrous root system and leaf veins in a parallel arrangement — think grasses.
Dicots, on the other hand, have a tap root system and leaf veins in a network (reticulated) arrangement, and yes, the jujube tree is a dicot.
Now the relevant part: while monocots and dicots have the same tissues visible in a root cross-section, these are arranged differently in monocots compared to dicots. (Dicot roots have an X-shape in the middle, while monocots have a ring instead.) I will be concentrating only on dicots in this discussion.
It would take me a week to draw something halfway decent and I don’t have a camera for my microscope (I really should think about getting one…!), so may I refer you to these excellent diagrams instead and invite you to follow along!
Let’s back-track briefly to last week and revisit the division zone immediately behind the root cap. This division zone is also called the apical (of the apex) meristem, though not at the very tip of the root (because of the root cap) as is the stem apical meristem at the very tip of a stem.
Bear in mind that last week dealt with the lengthwise distribution of specialised root cells. When reading the below, please also refer to the above-linked cross-section (also here) and visualise the two combined into a 3D structure.
Root Apical Meristem
As with the stem apical meristem, the root apical meristem is also where cell division and differentiation occurs. The apical root meristem further differentiates into three other meristems: the protoderm, which becomes the epidermis; the procambium, which becomes the vascular cylinder, or stele; and the ground meristem, which becomes the cortex and endodermis.
The protoderm meristem forms the epidermis, an outer layer of protective cells which also aid in absorption of water and nutrients. The root epidermis is also known as the rhizodermis. It is these cells in the maturation zone which produce the extensions that become root hairs.
The procambium meristem develops into the vascular (transport) cylinder, also called the stele, located at the centre of the root. The stele is comprised of xylem, phloem and pericycle tissues.
The xylem and phloem together are called the vascular (transport) bundle, and it’s the xylem which forms the distinctive X-shape in a dicot root cross-section.
Xylem transports water and dissolved nutrients from the roots up to the stems and leaves, and phloem transports food produced from photosynthesis (photosynthates) from the leaves down to the non-photosynthesising stems and roots of a plant.
The pericycle strengthens the roots, protects the vascular bundle, and can later develop into lateral roots.
The ground-meristem forms both the cortex, which is the region between the epidermis and stele, and the specialised endodermal layer which surrounds the stele. This layer is exclusive to roots and controls which substances can and cannot enter the stele — similar in a way to our own blood-brain barrier.
A waxy region on the endodermal cell walls called the Casparian strip forces water and water-soluble nutrients to pass through the endodermis rather than slipping between the cell walls. This same strip also excludes pathogens and toxins.
Having explored general root anatomy, next week we’ll cover what makes some roots produce suckers!
A plant root is an organ, and like all organs (plant or animal), has specialised regions marked by specialised tissue. This post outlines these, with an emphasis on the longitudinal section (a cut along the long axis) of a young, growing root. Next week we’ll discuss the regions and tissues in a cross-section (a cut at right angles to the longitudinal).
Specialised Regions of a Root
The specialised regions of a root are the
root cap (c in Figure 1 and 2 in Figure 2 below),
division zone immediately behind and within the root cap (1 in Figure 2 below),
elongation zone (5 in Figure 2 below), and the
maturation zone (includes the root hairs, h in Figure 1 below)
The root cap protects the end of the root as it moves through soil. Movement is aided by two actions of the cap. One is by the secretion of mucilage, a thick glue-like substance that lubricates the root tip as it pushes through the soil. The other is via production of carbon dioxide (CO2), which reacts with water in the soil to form a weak acid called carbonc acid (H2CO3). This acid dissolves some soil particles, which further makes it easier for the tip to push its way through.
The cap is comprised of a group of cells known as columellae (plural form of columella, column). (This has three meanings in botany, one of which specifically describes the longitudinal alignment of cells in the root cap — botany can be so precise!).
These columns are made of statocytes, cells which detect gravity via their organelles* the statoliths — removing a root cap causes the root to grow in random directions.
*An organelle is a cellular subunit — better-known examples include nuclei, chloroplasts and mitochondria.
The statoliths fill with starch and, being denser than cytoplasm, sink and deposit at the lowest part of the statocytes. This deposition initiates pathways that direct the root to downwards growth.
In addition to helping the root cap push through soil, mucilage also attracts beneficial microbes to the rhizosphere, prevents root cells from drying out, and glues soil particles to the root which aids in water and nutrient uptake. Mucilage can also contain compounds that inhibit the root growth of other species.
Root caps can also detect light and soil pressure to direct growth away and down into the soil, and can detect barriers and direct growth around those.
The division zone comprises the meristem and is a highly compact region, and together with the root cap is a centimetre or less in length. This is the growing region immediately behind the root cap and the columellae, and where new root cells are formed — only the root cap and the division zone of growing, dividing cells move through the soil.
In the elongation zone cells do not divide, but instead elongate to lengthen the root. This action also pushes the root tip through the soil. Further extension of this part of the root is no longer possible when these cells finish elongation and mature, and this section of root becomes stationary from this point on. A new elongation zone arises further down towards the root tip as a new group of cells develop behind the advancing division zone and the process repeats.
The maturation zone is marked by the development of root hairs — tiny extensions which increase a root’s surface area significantly and allow for higher absorption of water and nutrients, much as the microvilli in animal guts do. Root cells in this zone are no longer dividing but do grow bigger, causing the roots to thicken. Root hairs have a lifespan of a day or two, and break down at the proximal (plant) end of the maturation zone as new ones grow at the distal (tip) end. Lateral (side) root development also occurs at the proximal end.
This earlier post described the four branch types peculiar to jujube trees: primary (extension) branches, secondary (non-extension) branches, fruiting mother branches, and fruiting branchlets. Also mentioned were the two bud types, main and secondary, and that each could have either strong or weak vigour. The type and strength of a particular bud determined the branch type that developed.
The focus in that post was on terminal main buds (those at the end of a branch), and how the strong ones produce permanent extension branches that form the structure of the tree, while the weak terminal buds produce fruiting mother branches.
This week picks up where we left off, with the primary branches, but this time we’ll cover the non-terminal buds. That is, the buds along a branch rather than at its end, and what these develop into. And from there we’ll go on to discuss how the other branches form.
Normally the main buds along a permanent branch remain dormant while that branch’s terminal main bud remains strong and produces extension growth. When that terminal bud weakens however, and produces a fruiting mother branch, some of the main buds further down the branch will break dormancy and produce new growth.
A strong main bud along a permanent branch will produce a new permanent branch that adds to the overall shape of the tree:
A weak main bud along a permanent branch may also break dormancy and produce a fruiting mother branch:
Remember how a fruiting mother branch — which looks more like a pine cone than a branch! — is a bunch of very compressed shoots containing several main and secondary buds? If a main bud in a fruiting mother branch then comes out of dormancy, a new permanent (structural) branch will again form:
A strong secondary bud along a permanent branch will produce a secondary branch. This branch type has a distinctive zigzag growth, caused by the alternating nodes changing the direction of growth:
Secondary branches do all their growing in their first year, as the terminal bud responsible for growth dies by the end of the first year. While a secondary branch will survive for many years, its end will deteriorate back to a node over time, where it dies:
During the first year’s growth of a secondary branch, its secondary buds at each node will produce fruiting branchlets, while its main buds remain dormant. These main buds then break dormancy in the second year to produce fruiting mother branches.
Here is a current season’s secondary branch showing fruiting branchlets from secondary buds. We know this branch to be less than a year old by its colour and texture — predominantly reddening but with hints of green still present, and with the shiny, smooth look of ‘green’ wood.
Below are fruiting branchlets from newly forming fruiting mother branches on a secondary branch in its second year of life. Again the colour and texture age the wood as between one and two years old, in that it is slowly developing a more brown-grey colour and has a more textured surface. Unlike the photo above, where the fruiting branchlets come from buds almost flush with the secondary branch, these branchlets come from slight extensions which are the growing fruiting mother branches. These mother branches will extend a little further and look more like pine cones with each passing year.
And here are fruiting branchlets from fruiting mother branches on an older secondary branch, which is noticeably more grey than the younger branches above. Mother branches only grow a millimetre or so each year.
As mentioned earlier, fruiting mother branches will develop from weak main buds on permanent branches. However, most branches of this type will come from the main buds on secondary branches. As the fruiting mother branches are the ones to produce fruiting branchlets, this means most fruit will come ultimately from secondary branches — branches which do not grow after the first season. Something to bear in mind when pruning, a topic we’ll cover in due course!
Also mentioned earlier was that a fruiting mother branch is a group of very compressed shoots comprised of main and secondary buds. The terminal bud extends the growth of the branch slightly each year, for about ten years after which it is no longer productive.
Fruiting mother branches can produce up to ten fruiting branchlets in a whorl:
The fruiting branchlets themselves come from weak secondary buds in the mother branch. (As well as from weak secondary buds on secondary branches as mentioned earlier.) Please read this if interested in further detail on the anatomy of a fruiting branchlet.
A peculiarity of jujube trees is that the fruiting branchlets are deciduous and have mostly fallen off the mother branches by the following winter. Some occasionally remain on the tree but they will never regrow:
and come away easily if knocked.
And that concludes the discussion on jujube tree branch development!
Going further, this post breaks down the structure of a fruiting branchlet in more detail, while this post describes the anatomy of a flower in more detail. And this post documents a flower’s life from bud to fully open and ready for passing pollinators.
All we need (I think!) to conclude the whole branch-flower-fruit thing is the documentation of a flower developing a fruit — and that is definitely coming!
Around 7pm the other evening I was perusing my trees, and — as I often do, gently pulled down a fruiting branchlet above to look more closely with my loupe at the flowers and developing fruits along it. To my absolute horror it came away in my hand! I reconciled myself by thinking that maybe it was structurally weak and always destined to fall off, and decided to make good of the situation by writing about it!
So here it is, the anatomy of a Shanxi-Li fruiting branchlet!
This was a large branchlet, about 385 mm along a straight line, but closer to 405 mm long, as measured by following every bend of the stem with a piece of string and then measuring the string. It was so noticeably large (most in my experience tend to be under 300 mm long) that I really do wonder if it was structurally weak and would have snapped off eventually as the developing fruit on it grew larger and heavier?
As with all new jujube branch growth during a season, the oldest part of this branchlet (which was closest to the fruiting mother branch) was turning red while the youngest part of the shoot was still the bright green of new growth.
The proximal end (of anything) is that closest to the point of origin or attachment. Here, the point of attachment of this fruiting branchlet was the fruiting mother branch. Conversely, the distal end (of anything) is that furthest away from the point of origin or attachment:
Here is where the point of attachment was:
And here is the proximal end of the branchlet, with a transverse (crosswise, cross-sectional) view of the point of detachment:
A node is the point along a branch from which leaves and other branches grow. An internode is the interval between two nodes.
The closest node (and leaf) to the fruiting mother branch was 15 mm away. The largest internode, and the third along from the fruiting mother branch, was 40 mm long. The internodes were then spaced at 30 mm intervals, then 25 mm intervals, and finally the last internode was just 3 mm long, but with still developing leaves, and would have lengthened by season’s end. The penultimate internode was 10 mm long.
The leaves are alternate, meaning there is a single leaf at each node. The leaves alternate sides along the branch, because the nodes alternate sides, hence the name. (The two other leaf arrangements defined in botany are opposite and whorled.)The largest leaf on this branchlet was 90 mm long and 55 mm across the widest part. The smallest leaf was 35 mm long and 15 mm across its widest part. The very small, still developing leaves at the distal end were just 5 mm long.
The flower arrangement (inflorescence) at each node is a simple cyme. A cyme is a group of flowers in which the oldest flower occupies the end of the peduncle (the main supporting stalk, or main axis), and newer shoots come from the sides of that stalk.
As the flowers differ in age within a cyme, so too do the fruits which develop from those flowers:
And as flowers (and fruits) differ in age within a cyme, so too do they differ in age along a branchlet. Those at the fruiting mother branch (proximal) end are oldest and those at the (distal) tip are youngest. Here, these cymes which were closest to the fruiting mother branch have no flowers anymore, but do have the largest fruits. Note too the change in colour of the branchlet when moving from the proximal end towards the distal end:
The cymes at the very tip of the branchlet have the youngest flowers of all — minute buds which have only just begun development:
The cymes between these extremes occupy a gradient of mostly fruit and some flowers, to some fruit and mostly flowers, to mostly flowers and some buds, to mostly buds and some flowers. Note too the colour change along the branchlet. You can tell that the banchlet segment in the top photo below is closer to the fruiting mother branch than the segment in the lower photo below, as it is more red at the proximal end:
Fruiting branchlets are the only branches on a jujube tree to produce flowers and fruits — so writing about one allowed me to slip more botany in than I otherwise could have with another branch type!
To go further and discuss the flowers and fruits on a fruiting branchlet really require their own posts to do those topics justice. I covered Photo Journal: Anatomy of a Jujube Flower earlier, and fully intend to do one on fruit later, but here is a good place to wrap up this post with, I guess, a teaser for what will come!
The following photos are of the largest fruit on the branchlet discussed here. This fruit was the most proximal and 8 mm long.
Do revisit the flower anatomy post — this page may help too — and see if you can work out what the two little brown dots on this fruit’s distal end are. (Distal in this context refers to the end of the fruit furthest away from its point of attachment, and not to be confused with the distal end of the branchlet discussed above.)
What about now?
Yes, those are the two stigmata and the branched style of the original flower! The green fruit you see is the maturing ovary of that flower. But more on that to come later!
The proximal end of the same fruit reveals the sepal remnants:
Let’s (almost) bisect it. I say ‘almost’, as a real bisection would have had two equal halves, each with that delicate little peduncle cleaved cleanly in two along its length. Sorry but that was never going to happen!
Just looking at this you may well be able to make out which parts will become the seeds, the stone that contains the seeds, and the fruit itself? This, and what happens as the fruit grows, is definitely the topic of a future post!
Back here were lots of pretty pictures of jujube flowers, but not exactly much in the way of information as to what you were looking at.
As with that week, this week is another time-poor one I’m afraid. But while this post will also be photo-heavy, it won’t be as light on the words, and you may even be tempted to wander outside to examine your own flowers (jujubes or otherwise!) by the end of it!
Let’s first look at a stylised diagram of the parts of a flower. The flower in that illustration is a perfect flower — to botanists, that means it’s a bisexual or hermaphroditic flower, with both male and female organs, and able to reproduce on its own. More specifically, a perfect flower is one that:
makes and distributes male gametes (male sex cells, or pollen, the equivalent of sperm in animals)
makes female gametes (female sex cells, or ovules, the equivalent of unfertilised eggs in animals)
receives male gametes (pollen) able to fertilise the female gametes (ovules)
The third point is crucial as it is this capability that makes a perfect flower able to fertilise itself (though often with the help of pollinators such as insects or birds). Making male and female gametes is one thing, but if an ovule can’t then receive the pollen from its own flower, then that flower cannot fertilise itself.
I’m mentioning all this of course, because jujube flowers themselves are perfect flowers. Here’s a close-up of one. With reference to the stylised diagram, can you pick out the sepals, petals, anthers, filaments, bifurcated (branched) style and stigmas/stigmata (plural forms for stigma) in the jujube rootstock flower below?
(What you may think is the ovary is actually a nectary disc, which is above the (covered) ovary. See how it glistens with nectar?)
Here’s a different angle, of a Chico flower (this one’s nectary disc has finished secreting nectar):
How’d you go?
Probably the trickiest part is distinguishing those ever so tiny, delicate spoon-like petals from the petal-like sepals! You have to really look hard to notice them. And you have to look harder again to even notice the tiny anthers and filaments, which practically merge into the background and look like part of the petals at a casual glance.
It’s the sepals we see folded into the distinctive pentagonal shape of the flower buds:
And there you have it, the anatomy of a jujube flower — you’ll never mistake sepals for petals again, will you?!
And so as not to leave you hanging, here is a spent flower with the nectary disc and now visible ovary:
This week I thought I’d follow up on the last paragraph of this older post that had been getting some recent attention, as well as my comment under that post.
Fig. 1 below is the very same Lang referred to. This photo was taken on 19th October 2018, about two months after being potted into a 30 cm pot in August 2018:
Fig. 2 is the very same Li also mentioned, again two months after potting in August 2018, and photographed on 19th October 2018:
Both trees are of similar age, and you can see why I described the Li as ‘runty’ in that comment! It looks rather lost in that pot…
Fig. 3 below was taken a bit over a year later, on 7th November 2019. These are the same two trees in Figs. 1 and 2, side-by-side. The Lang (Fig. 3, left) and Li (Fig. 3, right) are in the same 30 cm pots of August 2018, and had been watered and fertilised similarly the whole time. They had otherwise not been disturbed (though I will pot them up next winter 2020).
The Lang at time of photo was about 110 cm high from base of trunk to tip of leader (longer if accounting for the angled growth), as marked. The Li was about 75 cm as marked (and longer again if accounting for the very angular growth!).
And Fig. 4 is the same photo, but showing how each tree had grown (or hadn’t!) by mid-spring 2018 and mid-spring this year 2019:
The Li is growing exactly as the Ta-Jan and Adrian’s Chico did. That is, it wasn’t, and then it was, with gusto!
But why was the growth of the Li (and Chico) so different to that of the Lang? To find out, we will need to zoom in closer on various branches and examine them —and if you’re not familiar with how these trees grow you are about to learn quite a bit!
But first a brush-up on some terminology to make this easier. Common to plant stems, irrespective of species, are nodes, the points from which leaves and branches grow. Some nodes are really distinct, such as the thickened rings between the segments of bamboo stem. (The botanical term for a segment of stem between nodes, regardless of species, is internode.) As leaves and branches grow from buds, buds are thus found in the nodes, whether or not they actually go on to grow a leaf or a branch.
Jujube nodes are unusual in that they contain two bud types: a main bud, and a secondary bud (Fig. 5):
And to mess with your head still more, whether such buds have strong or weak vigour determines the type of branch that will develop from them.
Pretty much every tree you’re familiar with has main branches and sub-branches that resemble each other despite age and location on the tree. But jujube trees really complicate things by having four different branch types: primary (extension) branches, secondary (non-extension) branches, fruiting mother branches, and fruiting branchlets!
The permanent primary extension branches are the ones that determine the shape and size of the tree. These branches are formed by terminal (end), strong, main buds which shoot each year and for many years to extend the tree’s overall structure and shape.
You can differentiate each yearly shoot extension along a branch — and thus age the wood — by its colour. Wood that grew two or more seasons ago is a drab grey-brown colour that becomes less brown and more grey with age. This wood also develops more furrows the older it gets (Fig. 6). (Thank you to Adrian for permission to use this photo!)
Last season’s wood is a smooth reddish brown. The transition between this and the prior year’s growth is very clear in Fig. 7 below. This wood will eventually become grey and develop furrows as it ages.
Current season’s growth is a bright green (Fig. 8).
The green will gradually change to the red colour of year-old wood by season’s end the following autumn. Fig. 9 shows this year’s growth on the Li of Fig. 3 above beginning to change colour at time of writing in late spring, 12th November 2019.
Some years later the terminal bud will weaken, the extension growth will halt, and a terminal fruiting mother branch forms instead of an extended branch.
Thus to summarise what we’ve covered so far: permanent branches are formed from strong terminal main buds, and fruiting mother branches form from weak terminal main buds.
Fruiting mother branches (not to be confused with fruiting branchlets, which we’ll get to!) aren’t only produced by terminal weak buds — they also develop from other bud and branch types which I’ll also get to — but let’s stick with the terminal buds for now as this is already getting complicated!
A fruiting mother branch resembles a pine cone. Like these two on the Ta-Jan in the earlier post that birthed this post (Fig. 10):
And these two on the same Li in Fig 3 above (Fig. 11):
And these two on Adrian’s Chico (Fig.12, and thank you again for permission to use this photo):
It is not at all obvious that these are branches, is it? Yet they are in fact very compressed shoots with several main and secondary buds on them. The (once strong, now weak) terminal bud of a fruiting mother branch grows ever so slightly each year, producing another cluster of buds that can produce up to ten fruiting branchlets in a whorl. The fruiting motherbranch is so named as it is the ‘mother’ of the fruiting branchlets, which are the dedicated branches for the flowers and fruits. The branchlets can vary from 100-300 mm in length (most fall within 120-250 mm in my experience), have alternating leaves on nodes 20-25 mm apart, and typically produce 3 or more fruits. These branchlets resemble compound leaves, but the presence of flowers and fruits show them for what they really are.
Fruiting branchlets are deciduous, and fall off by the following winter. On a small and young tree with little to no trunk/branch development, it is understandable to think your tree has died when you see every one of these little branchlets turn from vivid and healthy flexible green branches, to dried up, dead piles of brown twigs on the ground. Some branchlets do occasionally remain on the tree, but never grow again and come away easily if knocked or removed by hand.
Let’s revist the Ta-Jan. Below in Fig. 13 are the first and last photos of it in this post, side-by-side. Note how the main buds remained dormant while the secondary buds produced fruiting branchlets that growing season of 2017.
Yet the following year (2018) one of those main buds broke dormancy to produce this shoot, photographed on 10th November, 2019 (Fig. 14). You can tell from the red colour of the uppermost trunk that this shoot developed last season, in 2018. The secondary buds in the lower fruiting mother branches continue to grow fruiting branchlets — which are the same vivid green as all other growth of a current season.
If you go back to Figs. 11 and 12, you’ll see this exact same growth on the Li and Chico. That is, mother branches with secondary buds producing fruiting branchlets, but also where a main bud broke dormancy to produce a permanent primary branch.
But why did the Ta-Jan, Li and Chico all grow this way, while the Lang in Fig. 1 produced a permanent shoot structure from the outset? Here’s a close-up of the trunk of that Lang of Fig. 4 above, on 7th November, 2019 (Fig. 15):
You’ll see a fruiting mother branch at the junction where growth began in 2018. Unlike the Ta-Jan, Li and Chico, this branch simply had a main bud break dormancy in the 2018 season rather than this season 2019, hence the rapid growth readily apparent in Fig. 4. And while the Li in Fig. 4 put on its growth-spurt this year, the Lang has slowed in its extension growth, also shown in Fig. 4. It has instead developed more secondary branch structures.
There is already plenty here to digest, so I will describe these secondary branch structures and other peculiarities of jujube trees in a future post — and there is plenty more to describe when it comes to jujube branch development!
But to wrap up everything covered here:
Jujube nodes contain two types of bud: a main bud and a secondary bud
A bud may have strong or weak vigour, and this determines the type of branch that develops
There are four branch types: primary (extension), secondary (non-extension), fruiting mother branches, and fruiting branchlets
Terminal, strong, main buds produce the permanent primary branches, which ultimately determine the size and shape of the tree
Jujube wood is green in its first season of growth (less than one-year-old wood), is red during its second season (one-year-old wood), and subsequently browner then more grey and furrowed with each passing year
Permanent branch extensions cease when the terminal bud weakens; a fruiting mother branch develops instead
The (now weak, main) terminal bud of a fruiting mother branch will extend that branch’s growth slightly each year
Fruiting mother branches contain (usually) dormant main buds and active secondary buds that produce fruiting branchlets
A dormant main bud can break dormancy in a fruiting mother branch to form a new primary, extension branch