This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
As many of the finest perennial, and all those with an upright rhizoma, with the annual kinds, can only be propagated from spores, 1 will point out the ways by which we have been very successful with most of the delicate and rare kinds, both of the tropical and hardy varieties.
A seed pan (size immaterial) is filled to within one inch of the top with rotten wood and sphagnum moss, upon which is placed half an inch of light loam and leaf mold, with a liberal mixture (say one-fourth) of sharp sand, and a portion of sphagnum mixed up with the soil. When the pan is prepared, let it be well watered, and left in a shady place for several hours; after which the spores may be scattered upon the surface. The pan should then be placed under a hand or bell glass, (in a shady place in the hothouse,) and as much air excluded as is practicable by packing wet sphagnum round the bottom of the glass. Managed in this manner, the surface of the pans will not require watering for a considerable period, which will be found to be a great advantage, inasmuch as by frequent waterings many of the spores are disturbed and destroyed. It is very desirable to water as little as possible until the spores appear in the "Marchantia" form; bearing in mind that the soil must never be allowed to become dry, as that would be certain destruction to many of the more delicate kinds, after having been subjected to a damp atmosphere for any lengthened period.
Under the above treatment, more especially if the spores have been recently taken from a green specimen, most of the kinds will be certain to grow, notwithstanding twelve months may elapse before some of them may germinate.
Another method, and by which we have raised thousands, is to take some seed pans, in which place some half-decayed pieces of wood or bark, with a portion of soft friable loam and sharp rough sand well mixed together, placing them in any shady part of the house wherein ferns are grown, being careful to keep the surface always damp, and. the spores, which are constantly flying in all directions about the house, will germinate from time to time upon the surface of the pans, without any further care whatever. We have been successful in propagating many of the more rare and delicate species by this method, when all other efforts have signally failed.