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 :)
