This section is from the book "Commercial Gardening Vol2", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
To secure spores the fertile fronds of any particular species or variety are picked off the plants and placed in thin paper bags and labelled. The bags are hung up in some dry warm spot, and in due course the spores drop out of the cases and form a dark-brown dust within. The spores of all kinds of Ferns are very small and dustlike, hence great care is necessary not to sow too thickly.
As a rule, 5-in. pots (48's) are most favoured for sowing Fern spores, but other sizes may, of course, be used. The pots are well crocked to secure perfect drainage, and are filled up to within about 1½ in. of the top with good fibrous loam. On this a layer of finer and grittier compost, sterilized for preference, is placed, and made fairly firm and level with a piece of flat board. All the pots ready for sowing are prepared thus and then well watered with a fine-rosed watering pot. An hour or two afterwards the spores are sown as thinly as possible over the surface - a delicate operation that can only be acquired by practice - and a piece of glass is put over each pot. A place shaded from the sun is selected, and attention is given each day to watering. This is best done by plunging each pot into a bucket or tank of water so that the liquid rises from beneath upwards. In applying water overhead there is always a danger of washing the spores to one side of the pot and making ugly holes in the surface.