Most mushrooms reproduce asexually by releasing thousands of spores through their gills into the open air for dispersion into the environment. Every spore is capable of germinating to create a new hypha. Hyphae are masses of intertwined filaments of cells which are the morphological unit of the fungus. When a thick mass of hyphae forms it is called mycelium or mycelia. Mushroom mycelium is usually white in color with a rough, cottony texture. Root like growth is called rhizomorphic.

When spores germinate they consume the water and nutrients from their environment and begin to reproduce. The medium that mushroom mycelium grows on is usually called substrate. Before the mushroom can start to form fruit bodies the mycelium colonizes the substrate fully and when the environmental conditions are right the mushroom emerges to produce more spores.

A mushroom cultivator can take advantage of the rapid growth mushroom mycelium exhibits by introducing it into new, sterile substrates. The mycelium is so tenacious that a 10 cc culture syringe can inoculate 10 quart jars of rye substrate, the preferred medium of most cultivators, and those in turn can be multiplied up to 10,000 times their weight. The true potential of mushrooms has yet to be taken advantage of.
By: mike jones

For one ½ pint jar(~240 ml) you will need:
140 ml vermiculite
40 ml brown rice flour
some vermiculite to fill the jar to the top (app. 20 ml)
water

Put the required amount of vermiculite for all the jars of one batch (for instance 6 jars: 6 x 140 ml = 840 ml ~ 3.5 US cups ) in a bowl. Pour water slowly over the vermiculite while stirring with a spoon .Be careful to only put that much water in as it can be absorbed by the vermiculite. Stir it well so the vermiculite is uniformly soaked with water. When you tilt the bowl you should see just a little water starting coming from the vermiculite. This is when the correct water content is achieved. If there is too much water in the bowl, pour the wet vermiculite in a strainer and let the excess water drain for a minute. Then the vermiculite will be at the field capacity, which is perfect. Now put the required amount of the BRF (for instance 6 x 40 ml = 240 ml = 1 US cup) into the wet vermiculite at once and mix it in with the spoon. The goal is to uniformly coat the wet vermiculite particles with a layer of BRF.

Fill the mixture in jars ½ inch under the top. It's very important to fill the substrate in the jars without tapping it down at all. It should stay very airy and loose to provide optimum conditions for the growth of mycelium. Be careful not to leave any substrate on the upper edge of the jar. If you weren't careful enough and there are some substrate specks at the edge take a clean moist cloth. Otherwise contaminants can start at those spots and work their way down into the jar. Fill up the jar with dry vermiculite to the top. This layer hinders airborne contaminants reaching the underlying substrate in case they manage to come in during the inoculation and incubation. Take a 5in wide stripe of aluminum foil and fold it in the middle. Put the foil over the opening of the jar. If you're using jars with metal lids, you can poke 4 holes at the very edge of each lid with a small nail and hammer and screw the lid on. The holes should be slightly bigger than the diameter of the syringe needle.Fold the foil edges up and press them together so you get a nice aluminum foil lid. Then take a piece of foil measuring 5in x 5in in and put it over the first two layers (respectively the metal lid if you're using lids) leaving the edges of the foil reaching down, since it has to be lifted again during the inoculation. So now you have 3 layers of foil over the opening. The top layer is lifted during the inoculation.

Pour approximately 1in (2.5cm) of water into the pressure cooker, don't put in too much water otherwise it will come into the jars and alter their water content.
Then stack the jars into the pressure cooker. The use of a rack to keep the jars from directly touching the bottom of the cooker is strongly recommended.
Put the lid on and bring the cooker to the required pressure (15 psi = 1atm over atmospheric pressure) slowly over a period of 15 minutes on a medium flame.

If you heat up the cooker too fast this can cause the jars to crack.
As soon as the steam begins to escape the rocker or the vent at the top of the pressure cooker turn the heat back so only a very small, steady steam flow persists from the vent. From this point on, pressure cook for 45 minutes.
Depending on the pressure cooker model the cooking procedure works a bit different so if you're not familiar with pressure cooking consult the instruction manual or someone who used pressure cookers before.
After 45 min take the cooker from the flame and let cool for at least 5 hours or even better over night.
If you never used a pressure cooker before check out this document about the correct pressure cooker use.

If you are unable to find or buy a pressure cooker, you can also sterilize the jars using a big pot with a lid.
In this case steam the jars for 1.5 hours in a pot lid on. Use only approximately 1 inch of water at the bottom.
You might have to add some water to the pot during steaming due to evaporation.

Here you will need spores to inoculate your jars
After the cooker is cold to the touch take the jars out and place them on a clean surface, have an alcohol lamp or a lighter and the spore syringe ready. Shake the spore syringe to break up the spore clumps. To be able to shake it it's necessary that there is a small bubble of air in the syringe. If this is not the case, then you can suck approximately 1cc of sterile air into the syringe by placing the tip of the needle into the flame and slowly pulling the plunger back.

Loosen the foil from all of the jars so it can be lifted easily when you inoculate.

Take the cover from the needle and heat it over the flame until glowing red. Let cool for a few seconds

Take the upper foil layer off and put aside upside down.

Pierce the foil at the edge of the jar with the needle app. 1in(2.5cm) deep and inject the spore suspension towards the inner jar surface. You should see a small drop running down the inner surface of the jar towards the bottom. Each jar is inoculated on 4 equally spaced points. You should use 1 - 1.5 ml of the spore suspension per jar so one 10ml syringe is sufficient for 6 -10 jars.

Put the foil on again. Flame sterilize the needle again after inoculating 3 jars to prevent cross contamination just in case a jar wasn't properly sterilized. When all of the jars are inoculated fold the foil edges up and press them firmly together so you get a nice aluminium foil lid. Write the inoculation date and the species/strain information on the foil with an all surface felt tip pen. If you touch something other with the needle during the inoculation procedure except the foil surface of the bottom foil layer immediately flame sterilize the tip again.

To learn how to make a cheap incubator go toHow to Build a Incubator

The jars should be stored at 21-27°C (70-81°F), the warmer the better, but not exceeding 27°C. If you don't have these temperatures at home you can build an incubator to accommodate the jars.

Providing the jars are kept warm you should see the first sign of germination after 3-5 days as bright white specks. This is mycelium. If anything grows that is not white, for instance green, black or pink, then the jars are contaminated and their content must be discarded and your clean procedures need some improvement. After the jars are emptied and the jar is washed with detergent and hot water it can be used again.

Depending on the temperature and the viability of the spore syringe it takes 14-28 days for the mycelium to colonize the whole jar. Once colonized store the jars at normal room temperature, about 21°C (70°F) to initiate pinning.
Don't expose the jars to direct sunlight. Indirect sunlight (= the natural light that lights up a room because at day time out) or a low wattage lamp (cool white fluorescent lamp is ideal, incandescent lamp is less suitable) for 4-12 hours a day is sufficient.

/www.fungifun.org/images/pf/glas_bewachsen_klein.jpg" />
Within 5-10 days (with certain mushroom strains it can however take up to 30 days) pinhead-size accumulations of mycelium should form. These so called pins represent the beginning of mushroom growth. In the following days also small mushrooms with brown heads become visible. When this is the case it's time to birth the cake into the fruiting container where the mushrooms can develop to maturity. Some strains don't easily develop pins. In this case put the colonized jar wrapped in a plastic bag in the fridge over night and then proceed to fruiting next day, even if the cake doesn't show pins yet. This cold shocking usually helps trigger pinning somewhat.

Many different things can be used for a fruiting chamber, including camping coolers, aquariums, and large plastic containers (Rubbermaid brand or similar containers work great). The fruiting chamber must be at least 6-8" (15-20cm) tall, and have enough floor space for the cakes to be arranged with at least 1" (2.5cm) of free space on all sides. Spread the cakes out as much as possible so that the mushrooms have room to grow. If the chamber is much too tall or too large, it may be difficult to keep the humidity high enough. The bottom of the chamber must be able to contain water, and the lid must be somewhat airtight in order to keep the humidity inside high. Light must be able to shine into the terrarium. If you are using a cooler or non-transparent plastic container, you will need to cut a window into the top of it and seal it with some sort of transparent material so that light can get in but humidity can't get out. For this reason, glass aquariums make very nice fruiting chambers if they are kept at the right temperature range.

For the first week or two, the cakes will generally not do anything. Then, very small bumps, called "pins," "pinheads," or "primordia" will begin to grow out of the surface of the cake. These are the beginnings of mushrooms. Many will never grow any larger. However, some will grow until they are full-grown mushrooms. A mushroom is ready to be picked when the edge of the cap tears away from the "stem" (the stem of a mushroom is called the stipe). Often, there will be a thin veil between the cap and stipe. If this is present, you can wait until the veil tears before picking the mushroom. To pick a mushroom, grasp it near the base where it is joined to the cake, and gently twist it until it comes off. Immediately begin the process of preserving it, either by refrigerating it or by drying it, mushrooms will begin to rot immediately. Each cake will produce about 1-3 waves or "flushes" of mushrooms, normally with 2-5 days of dormancy between flushes. After about a month or so of fruiting, most cakes will be spent, and will not produce any more mushrooms unless rehydrated by dunking underwater for 24 hours, see dunk tek.

Some of the pinheads will begin to grow, then suddenly stop before they become full-grown mushrooms. These are known as aborts (aborted mushrooms). Aborts are just as good for eating as full-grown mushrooms, but they must be picked before they begin to rot. A mushroom that has mold growing on it or which has black goo in the center of the stem is rotten and is not safe to eat. It is often difficult for beginners to identify an aborted mushroom before it begins to decompose. Early warning signs include a halt in growth of the mushroom, and a greenish tinge around the dark colored tip of the primordia that will eventually become the cap of the mushroom. Always completely remove aborts from the cake, even if they are too rotten to eat, because they can get moldy and cause the cake to get infected.