How and when does a stem become woody?

Once a shrub such as a fuchsia has flowered, and the flower head becomes the fruit, what happens to the stems both leading to the apical buds and the pedicels? Does the remaining stem grow woody during the dormant period? Do all plants gain bark, even grasses?
In this photo of a fuchsia, what will happen when the red fruits have gone? When te stem dies down in autumn, will it re-emerge woodier, and longer, with more buds? Do the pedicels become woody themselves?
http://pics.davesgarden.com/pics/wallaby1_1153920009_574.jpg

 

Hi SimonZ. Plants can be divided into two groups - woody and non woody. The non woody ones are called herbaceous - which is where we get 'herbs' from - but that word is often hijacked to mean other things such as used in cooking. Herbaceous plants grow fresh, non woody, stems and vegetation every year, and then die back completely in the winter. In the spring they grow again from scratch. Consequently they never become woody. Most grasses fall in this category, but Bamboo is a grass and does get woody - possibly in the second year?

Woody plants are generally called shrubs and trees. The foliage may die back in winter as in leaf fall from trees, but the stems ie trunks and branches don't. In the second year when they resume growth, they build on previous growth. Wood is nature's way of building strength into a stem, to make it more rigid as obviously things that build on the previous years growth are potentially capable of growing very tall.

A Fuchsia is a small shrub - because it builds on last years growth and grows woody. And many other garden plants such as Penstemon are also technically small shrubs, as they too go woody. I think they grow the wood during the second and subsequent growing seasons, as they need it for strength. During the winter I suspect most Fuchsias go dormant if they are outside and lay down very little in the way of cells. In practice a lot of plants lie a bit between the two, and it may well be possible for plants to get a bit woody in the first year if they grow big enough.

Wood (secondaty xylem) will be laid down wherever there is previous years growth, but as a pedicle is a flower stem it will be lost with the flower and won't carry on to next year.

 

Many thanks for your informative answer. Does this mean that each year the actual pedicels slowly disappear? Or if the woody stems & branches remain (and are not pruned), where do the next year's buds grow? Does the stem get taller every year?

 

The pedical is the flower stem, and is essentially part of the flower. Once the flower has done its bit, the unwanted parts will fall off. The pedicle will be the last to go as it will be supporting the ovary and seeds. But once the seeds have been dispersed I suspect that it will be made redundant as well.

There are hundreds of latent bud positions in something like a Fuchsia under the bark, in the woody parts that just look like dead sticks in the winter. But come spring you will see loads of tiny buds emerging from the wood. I think that the older the stem, the thicker the wood and the less buds there are. So most of the buds will be on the previous year's wood but there can still be some on older wood. You can see this sometimes on a tree, you can still get small leafy growths from the trunk of huge tree, although most of the new growth will be at the top of the tree.

In a tree the new growth is on the outside, leaving the centre of the tree to be essentially dead. So the outside of any plant will presumably have the potential to sprout new shoots. But a lot of plants don't like to do it on very old wood.

Most plants tend to grow up to a natural height. But that can be a lot higher than you think. We are used to trees growing to 60 or 100 feet because they live a long time. Many woody garden plants, if they live long enough, can grow quite tall. But they are often not allowed to, because they either get killed by the cold or cut back.



I am sure Victoria won't mind me using her picture above of Poinsettias, which are perennials, in her garden in Portugal. We are so used to seeing them one foot high at Christmas that we don't realise that under the right conditions they will grow to seven or eight feet high!

 

Thanks for that reply Peter, and for the photograph. I suppose what I'm still stuck on is where the actual new year's growth comes from, and how a shrub or tree extends its stems and branches every year. For instance, in layman's terms, if I am the apical bud, will I still be the apical bud next year? Or when the new growth happens, will the extended stem outstrip me and have new buds? I assume all the buds which have flowered or put out leaves, etc, will still function the next year? The plant in your picture, for example: would it's existing stems just grow longer with the same buds, or do new stems grow as if added on to the tips of the old?
I do appreciate the time you have taken to answer my rather clumsy questions!

 

I wondered whether that was what you meant Simon. I will try an explain what I understand to be the mechanism. But first you must recognise that plants vary in their mode of growth, if they didn't they would all look the same.

A seedling has a stem and at the top there is the apical bud, which as you know is the prime growing area. There is a thing called apical dominance, where the apical bud caused chemicals to be produced lower down the stem that inhibit, to a greater or lesser degree, secondary buds from developing. A Fir tree, for instance, has strong apical dominance. The main stem just keeps growing and growing, with few side shoots. But an Oak tree has weaker apical dominance. After it has produces a trunk, it bushes out at the top.

A seedling grows till it produces a node - a pair of leaves with potential secondary buds between the leaves and main stem. But apical dominance will stop the secondary buds developing. The apical bud will then continue to grow until it creates a second node (I have no idea what makes it produce a node). This unit of growth, between nodes, is called an internode. The apical bud consists of a top bit and just below is an area where cell division takes place. So the plant growth takes place in this area - just below the tip. The plant will continue to grow by two different means. At the top the apical bud will continue to add new units of growth - ie new internodes. But lower down, the existing internodes will elongate. They can do this two ways, either by cell division - ie creating more cells, or by cell elongation ie the cells getting longer. I saw one reference relating to a Helianthus where the internode elongated 65 fold, of which 13 fold was due to existing cells lengthing and 4.5 fold due to new cells. But it varies from plant to plant.

When winter comes, the apical bud may become dormant, but is still alive and will continue in the new year. Thats how a Fir tree grows straight up for many years. However if the apical bud is removed or damaged, it stops creating the chemicals that suppress the buds lower down, and consequently they start to grow. That's why pinching out the leading tip will make a plant bush out. Apical dominance is never 100% so plants naturally bush out a bit. How much depends on the plant in question. If the apical bud turns into a flower bud like a sunflower, apical growth ceases.

So, to answer your question, some plants are capable of growing straight up, by a combination of the apical tip producing new units of growth - ie new internodes, and the elongation of existing internodes. However if the apical tip is damaged side shoots will take over. In some plants apical dominance will persist during the life-time of the plant, but I think that in many plants it disappears naturally after a while. Walnut had been telling about Brugmansias in his posts. They apparently have apical dominance for several feet, and then automatically branch, and they cannot flower until this branch occurs. It appears that chemicals are released after a time that both remove the apical dominance and also start the flowering process.

Thank you for your question. I always like to understand how and why things work, its much easier to remember what plants do if you know why they do it. Its also useful to think through a process as it forces me to do a bit of research and in the process learn a more myself.

cheers Peter

 

Thanks again, Peter, I really appreciate your answers, and any input from anyone who can help. I am studying Horticulture at the moment and a little foxed by some of the biology, though I am trying to phrase my questions as simply as possible.

I asked a similar question on Yahoo Answers, and the reply (also curiously from a user called Peter S!), stated that with the stem's elongation, a new apical bud would form. What I wish to know is if, for example, I were to dab the edge of the apical bud with a blob of paint, when the plant grew next year, it would be that same apical bud with the same blob of paint, or if it would have died, or just been "relegated" further down the stem. Or perhaps this differs from species to species?
If apical dominance prevents axillary buds from flowering, is it something that only lasts a single season (as in your example of a sunflower)?

In this picture:

http://www.cactus-art.biz/note-book/Dictionary/aaa_Dictionary_pictures/Apical_and_axillary_bud.jpg

would the plant increase the following year by having 4 pairs of opposite leaves instead of the current 3, and if so, would it be a case of the toppermost pair moving up, or a new pair forming above?
Similarly, I am growing Crocosmia x crocosmiiflora and at present there are 8 pairs of buds beginning to flower. Next year, should I expect 9 pairs, or the same 8 - or perhaps it is not as predictable as that?

I am assuming that when a tree branch elongates, new growths emanate from existing ones, and the terminal buds are new, which is why the latest growths always appear softer or greener than the twigs preceding them?

I see you live in Harrogate. One day I will visit the Botanical Gardens there - it looks very beautiful indeed.

 

My understanding is that if you put a spot of paint in the top of the apical bud of say a fir tree, you would see that paint spot lifted into the air and a few years later it would be 60 or 100 feet in the air, still at the very top.

A fir tree is a bit like a building. A bricklayer (the apical bud) sits on the top laying bricks, and he moves up with the bricks. Every now and then he completes a new story ( a node) and lays down joists and floorboards etc. But he does this from above as there is nothing above the bricklayer (the apical bud) except for his hard hat (a layer of cells with some bud leaves that protect the apical bud).

So the top bricklayer is building new stories (ie internodes) at roughly equal intervals at the top of the building. But at the same time a team of extension builders have moved into the lower stories and are stretching them upwards (internodal elongation). If the top builder builds stories at intervals of say 10 feet. In the case of the Helianthus mentioned in the previous post, the lower internodes were stretched 54 fold. That is the equivalent of the team of extension builders stretching the bottom story upwards from 10 feet to 540 feet. They do this from inside the building, making it taller. But the top builder is still sitting on the top, but now much higher off the ground than he was before. I wouldn't have thought that stem elongation (ie the team of extension builders inside) would have any impact on the apical bud (ie the bricklayer at the top). They are in different parts of the building.

I don't think the top builder (apical bud) is ever relegated lower down the building (plant) because there is no way of building anything above the top builder. The only way he can be relegated is if he falls off his perch (ie the apical bud gets damaged and stops building or just slows down) and another tower alongside grows faster and taller (ie a side shoot overtakes the main stem). Incidentally this second tower will also have a builder sitting on top of it laying bricks (ie another apical bud).

So in your picture, if you numbered the pairs of leaves 1,2,3 in the order that they appeared, 1 would be at the bottom with 2 and 3 above. The next pair of leaves would be 4 and they would be at the top. This way the top of a plant is always the newest and the greenest, and the old part at the bottom becomes woody.

Whether the apical bud is exactly the same one as at the bottom is a somewhat philosophical question. Is your skin the same as you had as a child? The chances are that the cells themselves have been replaced, but in principle it is the same.

Apical dominance is capable of lasting several years, but in many plants it reduces with size and time. If it was there all the time, all plants would look like Fir trees, and if there was no apical dominance every plant would form a symetrical mound. Most plants are between the two.

I have described the growth upwards, above - assuming only one apical bud. But when there are buds that develop lower down, they will follow exactly the same pattern. Each new growth will have a new apical bud. So a tree branch will grow in exactly the same way, but sideways. In fact all growth must follow the same pattern.

Crocosmia is not really relavent as it is herbaceous. Ie all growth above ground will die and it will grow from scratch again next year. What it does next year will be a bit different from this year because the temperature and rainfall will be different.

 

Many thanks for that. I am beginning to understand it all a lot better now, for some reason this whole area has been on my mind recently and it is starting to appear much more clearly. Yes, Crocosmia was a silly choice of example (I had been making these posts in a slight rush during lull spells at work, where I have also been sounding out the horticultural knowledge of long-suffering colleagues!).