The life cycle of ferns produced from spores is of interest in understanding how to propagate them.
Life cycle of a fern:-
"Wrigley and Fagg’s" "Australian Native plants" has a good section on the life cycle. I have the third edition, and a lot of the following is taken from pages 39-40 of this book.

Many ferns that reproduce from spores grow in very sheltered areas such as gullies where there is plenty of constant moisture. Also they is very little physical disturbance from direct rain or wind.  Moisture usually comes from water seeping down into the gullies, or from mist.

Groups of spores (sporangia) are produced in the sori (groups of sporangia) on the underside of fronds. These germinate to form the sexual stage of the fern, known as the prothallus. The prothallus is a flat green structure, looking (very roughly) heart shaped and smaller than a one cent piece. Male and female re-productive bodies are then produced and in the presence of water, unite to form the asexual stage, which is the fern plant as we know it with roots and green fronds.

It is important to note that the male re-productive bodies, i.e. the sperm, actually swim to meet the female re-productive body. Therefore one of the most important factors is the presence of constant moisture. In the wild, although many spores are produced, very few of these actually grow up to become mature ferns. Indeed, if you have the right conditions in your garden/shade house, or any sheltered spot on you property, that has constant moisture for enough time, spores can germinate by themselves.

Note :- It is worth noting that most ferns have prothalli that have both male and female sexual parts, however "Fairley and Moore’s" "Native plants of the Sydney District" tells us that ferns of the Marsileaceae and Azollaceae families (Marsilea and Azolla) are "distinctive biologically as well as structurally since, unlike land ferns, they produce micro and macro spores that germinate and grow into separate male and female prothalli."

My method of growing ferns from spores:-
Once again the main things to remember for successful propagation is that we need constant moisture, in a sheltered environment. Also to ensure success it is best to have a reasonably sterile environment.
The first thing is to collect the spore. You can see spore sacs on the underside of many species of ferns. The arrangement of spore sacs can be in rows, it can be a stripe on the edge of the frond, or it may appear to be brown dots in a regular fashion. When ripe, the spore cases are usually brown. To collect the spore, just cut the frond and put it into a paper bag. After a week the spores should have released from the spore sacs, and will be a brown "dust".

Next, prepare the container to put them in. We need to provide water from the bottom, and the top of the container needs to have a cover to keep in the humidity, and to prevent moulds, mosses and airborne bacteria from getting into the mixture.

Also we need to sterilize the mixture. I do all this by using a seed tray, with 6 cubicles, and I place this into a rectangular chinese food container, with a little bit of river gravel on the bottom (so that water can come up through the holes in the bottom of the seed tray). In this tray is the soil. I experimented by using Beresford park seed raising mix, Lush growth potting mix, and 50/50 sand pet moss mix, all in the same tray (in different cubicles). All mixes worked, so the type of potting mix used is probably not critical.

With the mixture in the seed tray, which is in the food container, I pour boiling water onto the soil, and onto the lid of the food container. I then put the food container lid onto the seed tray (to provide a sealed environment), and leave it to cool down. When this has cooled down I sprinkle the spores lightly over the mixture, and put the lid back on.

We have now provided an environment that is sterile, and humid. I keep this container inside near a shaded window that gets morning sun. However a shade house would probably be a better spot to put this (dappled sun). Just ensure the container has some water in the bottom, and the spores will germinate within 6-8 weeks.

When the spores germinate you will literally have hundreds of green organisms. Wait till you can see the tiny organisms develop into the roughly heart shaped prothalli, and at this stage there should be overcrowding. Carefully prick them out into other containers, prepared as above, with more than one prothalli together (so that they can fertilize each other), or just thin out the existing seed tray.

Just carefully place the plants into the soil mixture, don't cover them with soil. Once these prothalli are fertilized you will see small fronds develop.  I keep these plants in the seed trays with the lids still on, until the fronds start to touch the lid. When this happens, I simply take the lid off, but keep them in a sheltered position, continuing to water them from the bottom. They might need further thinning out at this stage. These plants can be left in these trays until they are too big, then potted out, and they can then be watered from above.

Plants propagated from this method do take a long time to become large plants, but you are assured that you will get a very large amount of plants. All of the tree ferns can be beautiful house plants from a young age, and it is very rewarding to be able to grown plants this way.

Because the plants are watered from below, when young, you can forget about watering them everyday, as the water only has to be topped up every now and then.

I hope that some of you out there will try the above method. So:- go forth and propagate!!!