Flower anatomy

So I'm going to chicken out here, and only cover floral anatomy. Mostly because I'm a little tired and pressed for time at the moment. Will put up the mechanics of fertilisation in the next post probably.

Basically a flower is there to ensure pollination, so a fertilised seed can be produced.
There are many types of floral anatomy, and it's too complicated to go through them all, however most plants conform to a single type, and have basic variations on that theme.

I'll run through flowers that have both the male and female parts, although as mentioned in the last post, not all flowers do.

Right. Diagram time (wooo paint, because I don't have photoshop on this computer!):

(not bad for a paint job, hey?!)
The parts of the flower and their function are outlined below:

Petal: Can be bright and colourful to attract pollinators. Can vary in size, shape and colour depending on what the plant is trying to attract, if anything at all. Usually in plants that are not trying to attract anything, they're reduced in size and dull in colour, if they're even present at all.

Sepal: (The green bits at the bottom of the Petals) Together they make up the 'Calyx', functionally they may be there purely to protect the flower (while in bud), or they may be specialised and look like petals. For example most orchids have a specialised Calyx that looks like petals. Dasies are another example - the center of the daisy is actually hundreds of tiny flowers, while the 'petals' are actually a specialised Calyx.

Receptacle: Is basically the base of the flower, it is the part where most of the other components are anchored.

Peduncle: The stem of the flower, from the base of the Receptacle right down until it attaches to the branch it's growing on.

 Now the reproductive bits:

Female parts:
Stigma: The part that catches pollen for fertilisation, and part of the Pistil of the flower. Usually it's sticky and pollen-catching only when receptive to fertilisation. Because of this, if the plant splits up when the male and female parts of the flower are mature, the plant can often avoid many of the problems of self-fertilisation.

Style: The stem the Stigma sits on. This can be long or quite short, together with Stigma and Ovary comprises part two of the Pistil.

Ovary: Found at the base of the style, the Ovary contains the female reproductive parts of the plant, the Ovules. The whole structure from Stigma to Ovary makes up the Pistil. The structure of the Ovary can be quite important for identifying plants; it can have one to many chambers, it can sit above the place where the Petals/Sepals/Stames attach to the Receptacle (superior Ovary), halfway down where they attach (semi-inferior) or below where they attach to the Receptacle (inferior Ovary - perhaps I'll put diagrams up sometime to make that clearer!)

Ovules: Again, there may be one or many hundreds of thousands of these, each having the potential to become a new seed. Not all will be successfully fertilised, think of a pea pod. Sometimes you get those tiny little not-developed peas in there? They're probably aborted seeds, or those Ovules that simply haven't managed to be fertilised.

Male parts:
Anther: The pollen-containing part of the flower. Usually the Anther will split open on maturity, releasing the pollen to allow it to be either carried away by the environment or an animal. What axis the Anther splits open on, or if the pollen just moves through pores etc, is often family or genus specific and can be taxonomically useful.

Filament: The stem that the Anther is found on. Together they make up the Stamen, and this can vary in size, number, shape and position in the flower. Plants that want to avoid fertilising themselves might have the Anthers below the Stigma, to stop pollen from the same flower getting to the Stigma. Or they might have Anthers that sit above the Stigma, but mature either before or after the Stigma becomes receptive to pollen.


So that is basic flower anatomy. Pollen is released by Anthers, aiming to get stuck on Stigmas. But you may have noticed that the Stigma is a long way from the Ovules in the Ovary? How does the pollen get from being stuck on top of the Stigma to fertilise the Ovule in the Ovary? I'll tell you in the next post ;)

Time to give this blog a reboot I think. So a post about the alternation of generations in plants

So my posting went from semi-regular to irregular to nonexistent. Apologies.

So in order to give it a kick in the pants, I think I'll write about... pollination. Or perhaps first the different types of reproductive methods found in the plant kindgom, then end with a post regarding pollination. It's a little complicated, so might take a couple of posts, but at least I haven't covered that yet! I might actually start with the confusing part, which is a process known as alternation of generations, because understanding that will make understanding plant reproduction a whole lot easier.

So, there are several kinds of plants, which are generally thought of at differing evolutionary levels.
Going from the most 'primitive' to the most 'modern' you have the Non-Vascular plants, such as mosses (Bryophytes), the Seedless Vascular plants, such as ferns (Pterophytes), then there are the higher plants which are made up of Seed plants such as connifers (Gymosperms) and finally the Flowering plants (Angiosperms).

Each group of plants has evolved its own way of solving the problem of reproduction, with each level seemingly involving more and more complex structures in order to do so. But first I'll talk about alternation of generations, otherwise known as the alternation of phases or metagenesis. But I know it as alternation of generations ;)

So what does that even mean?
Well, in short it refers to which tissue type (or rather, what that tissue is derived from) makes up which part of a plant's lifecycle, and whether or not this can be easily separated into two separate generations. It was 'discovered' (read: described) by Wilhelm Hofmeister in the late 1800s, and shows clearly why the reproductive structures we see today are necessary for the funtion of the various reproductive methods.

Edit: First a couple of definitions to help out:
Haploid: Cells that contain a single set of chromosomes (n).
Diploid: Cells that contain two sets of the same chromosomes (2n), ie paired chromosomes
Meiosis: The division of a cell whereby the chromosomes do not replicate, resulting in one of each pair of chromosomes occuring in each of the new daughter cells (ie produces 2 haploid (n) cells)
Meitosis: The division of a cell whereby the chromosomes do replicate, and each daughter cell has a pair of each chromosome (ie produces 2 diploid (2n) cells).

There are two basic phases that plant tissues go through. The first is the Sporophyte phase, which is diploid (like us it has 2n chromosomes) and the second is the Gametophyte, which is haploid (has only n chromosomes). Depending on the organism, one phase is usually dependent on the other for surivival, however ins some plants (eg Ferns) the two stages may be capeable of living independently. Following so far? Good :)
The Sporophyte, perhaps unsurprisingly, produces spores, whereas the Gametophyte (also unsurprisingly) produces gametes.

So how does this happen? Well:

The easiest place to start with this is the Sporophyte.
Like I mentioned before, the Sporophyte is diploid (2n), and in most plants it forms the largest and most long-lived part of the lifecycle (for example every part of a tree you can see is the Sporophyte). In Bryophytes (mosses), it's the other way around, and the Gametophyte is dominant, with the Sporophyte only appearing in time to reproduce. In either case the reproduction is what we're interested in here. So selected cells in the Sporophyte undergoes meiosis, and split into 2 haploid (n) cells. Meiosis differs from meitosis in that there is no replication of the DNA within the cell, rather the chromosomes halve in number when the cell divides. So this process produces spores that are haploid, and that will form the basis for the next stage of the life cycle.

The spores then either disperse or don't (depends on the plant) and develop into a haploid Gametophyte stage. In Bryophytes they usually do disperse, and once they have done they grow into the new Gametophyte. The Gametophyte produces gametes through mitosis (remember, the Gametophyte is haploid so must undergo mitosis or the number of chromosomes would be halved again, which would be disasterous!) and depending on the the structure they're produced in, and the plant we're talking about, these are usually different sizes. The male is generally termed the 'microgametophyte' and is a motile sperm (ie it can swim towards the egg), and the female the 'megagametophyte' and is usually a sessile egg (ie it stays still).
Again, depending on the plants we're talking about, these can be produced in specialised structures (in mosses for example the male structure is the antheridium and the female is the archegonium). If fertilisation occurs, the mirco- and megagametophytes fuse and form a new diploid (2n) zygote, which will grow into the new Sporophyte generation and the whole cycle can continue again.

Edit: A picture to help out (because I finally drew one). Using Mosses (Bryophytes) as an example

 

Phew. So that in a nutshell is a brief (and I hope not too confusing) explaination of the alternation of generations in plants. I think that's probably enough to absorb right now, so I might explain how seed plants and flowering plants all fiddle with this in the next few posts ;) Also if I'm really motivated, I might even do some diagrams to try to help explain this a little better (edit: yay! Did that!).

Also if there is a topic you would really like to discuss, leave me a comment and I'll see what I can do about that. I promise nothing (hell, I'm not an expert in any particular field anyway!) but it never hurts to ask :)

A word on water potential

So it's time for the first of the physiology posts.

Water is essential for all life on earth. Without a plentiful supply of it, we certainly wouldn't be here. Plants originated in aquatic environments, and one of the many challenges they had to overcome when they made their move onto dry land was how to obtain water. They cannot actively drink it like we can, so a way to passively move water from their roots to the stems evolved.

In order to regulate the water within their tissues, plants use pressure gradients. Because water will always flow from an area of high pressure to low pressure, by creating a pressure gradient in the tissues of the leaves water will be drawn into them from the stem, and into the stem from the roots. In this way, the whole plant becomes a pressure gradient - the roots always have the highest water potential, followed by the stems and finally the leaves. By opening and closing their stomata (pores on the leaf surface), water can leave the plant, and the gradient can continually function (otherwise the water would build up in the leaves, the pressure would increase and the gradient would eventually stop).
During drought of course the plant conserves it's water by closing the stomata, and usually the water potential of the whole plant decreases. If it continues without water for too long, leaves wilt and the plant eventually dies.

So, the underlying question about all this is how does the plant create different pressures in its tissues? There are two basic ways to achieve this. Firstly, you can change the volume of the plant cell, without altering it's size (think of a bottle of fizzy drink - if you shake it and the gas leaves the drink but you've not opened the bottletop, the bottle becomes highly pressurised), or you can pack the interior of the cell with solutes such as salt, and water will be drawn into it. Typically plants use solute loading to decrease and increase their water potential, taking up salts such as potassium from the soil and ground water.

In a nutshell, plants can use water thanks to basic physics. They can regulate their water use through a variety of mechanisms, all of which are vitally important for the plants photosynthesis and survival. An important component of why plants water regulate the way they do is a need to balance water loss with the uptake of the carbon dioxide necessary for photosynthesis (which occurs when stomata are open). So this will be the subject of the next post :)

Firstly, to science!

The inspiration for this particular post is two-fold. I'd been intending to write something along these lines for a while, but hadn't so far gotten around to it. Considering Easter has just come and gone, and there was, shall we say an 'enthusiastic', debate on a particular TV show last night it has prompted me to actually do it.
Writing about the scientific process, and science as a 'new religion' I think is a good starting point for this particular blog. So here we go!

First and foremost, science is a process. It is a methodology used to uncover information about the world around us, and to discover how the systems within that world function and interact with one another. It is not about proving things to be true, or about dogma (usually - although in some disciplines it does sneak in with some theories) but instead is about experimentation and discovery of the most plausible explanation available at the time, and the ability to switch to an alternative and better explanation should one ever arise.
In this, is the core of the power of science.
Because of the way science functions, better explanations for phenomena are always sought. Dogma rarely takes hold, and if there is insufficient evidence to support them, theories do not progress very far. Even widely accepted theories, even those strongly supported over such a long period of time as to be called the 'laws' of science, are continually being put to the test. E=MC(squared), Einstein's famous equation used to explain the relationship between mass, energy and the speed of light (in a vacuum at least) is now again under scrutiny, as are the theories of gravity (well, talk to any quantum physicist about that one), evolution by natural selection (microbiologists, geneticists etc) and Netwon's Laws (those quantum physicists again). That is not to say those laws are now seen as 'untrue' and will be scrapped - far from it. The beauty of science is to continually progress such laws, adjusting them accordingly as new knowledge is gained.
Those who state science is the new religion have no understanding of what either 'science' or 'religion' actually mean, nor what they stand for. Equally, those who boldly state that 'science will eventually answer all our questions' also do not understand the scientific process, nor how it functions within our society. These are two reasons I refuse to give science the capital S that many do (aside of course, from when it is at the beginning of the sentence).

Take, for example, a simple experiment. We're growing tomatoes, and want to know if we add fertiliser twice as often, if they'll grow better/produce more fruit (bear with me, I am a botanist and this is the first appearance of plants in this blog!).
The scientifically designed experiment you'd use, would be to have two 'treatments'. One you could give lots of fertiliser to, and the other none (or much less - termed a 'control'). Then, once they have fruited for whatever length of time you choose, count or weigh the produce and compare the two. It might be expected that the one with more plant-food did better, and for the sake of this example let us say that this is indeed the case.
The purpose of science, however, is not to simply find out whether things are 'true' or not, but also to attempt to explain why they are so. In the case of the tomatoes, the first thought you would have would be that they extra nutrients allowed the plants to produce more fruit. However this may not be the actual effect the nutrients had. There could be many other factors that accounted for this extra fruit, and these are known as variables.
Perhaps the pots the tomatoes were planted in were placed in patchy light? If those with the higher nutrient treatment happened to have more light (due to chance) than the others, this, rather than the nutrient levels, may explain their increased fruit set. If they had more light, they'd also have likely been exposed to higher temperatures, as it gets hot in the sun. Or it could be something else - perhaps the extra nutrients allowed them to grow more roots, take up more water and then produce more fruit? Or perhaps it was some other chemical or biological process, such as the particular blend of those extra nutrients allowing a particular beneficial microbe to grow in the soil with the plant, and hence increase the fruit production. Or the presence of the fertiliser may have changed the pH level of the soil, and allowed previously inaccessible nutrient sources to be 'unlocked' for the plant by changing them to a different form. Any one of these explanations could tell us why higher nutrients caused a greater fruit set, and each could have it's own experiment set up to investigate it. Or, better yet, the scientist would have had some ideas as to why nutrients would work before they started, and would have built tests for some of these factors into the original experiment (known as 'controlled' variables).

So from this terrifically simple example, you can see how complicated science can get. Without the question of 'why' as well as 'does', we could easily conclude that the additional fertiliser works because fertiliser is magic, and our knowledge of the system would barely increase at all. The point of this example is to illustrate one of my favourite aspects of science. Think of it, if you will, as the mythical beast, a hydra.
Chop off one head, or answer one question, and another two will appear in it's place.
This is the fundamental reason that science can never answer all our questions. But in the past few centuries, and certainly within the last one, our scientific endeavour has brought us so very far. Our knowledge base is rapidly increasing, and the rate of new advancements in science is also accelerating. Having said all of this, I don't see our hydra situation as a problem. As our knowledge increases, so does our want to learn. Learning is good for us, if we didn't learn we would still be monkeys sitting around in trees in Africa (well, there is another contested theory - the 'out of Africa' theory). And yes, I know monkeys can and do learn but you know what I mean.


In a nutshell, science is a remarkable process by which we learn about the world around us. It is not some god worthy of worship, nor does it attempt to be. It is a tool we use to understand the universe we live in, and hopefully one that will allow us to improve our lives and the lives of those to come.