Herbaceous or shrubby plants, sometimes attaining the dimensions of trees in the tropics and the temperate regions of the southern hemisphere. Stem when erect simple, but as a creeping rhizome often branched. Leaves (here termed fronds) tufted or alternate, simple or more or less divided; vernation circinate, or rarely straight as in the Ophioglosseae. Petiole or stipes continuous or jointed, rachis or midrib often grooved above. Fructification consisting of minute capsules of spores borne in clusters (sori) on the under side or edge of the fronds, or sometimes on separate fronds. Sori naked, or covered with an orbicular peltate reniform linear bivalved or urceolate involucre or indusium. Capsules or spore-cases sessile or stipitate, frequently intermixed with bristles, or imperfect spore-cases. Ferns inhabit nearly all climes, but they are rare in very cold and arid regions, and attain their greatest development in tropical and temperate countries possessing a humid atmosphere. There is a wide divergence of opinion amongst pteridologists as to the number of genera and species. Sir W. J. Hooker, in his 'Synopsis of all Known Ferns, reduces the number of genera to 75, containing about 2,500 species; but other authors, who are content to establish genera upon much more slender characters, raise the number to above 200, with a corresponding increase in the number of species. It is a fact beyond controversy that Ferns are equally as variable as any other class of plants, and this tendency to variation is well exemplified in our native species, without including the numerous pretty though abnormal forms which have increased so vastly in cultivation during the last twenty years. With the exception of a few species from Northern Asia and North America, and perhaps a few from the southern hemisphere, we are limited to our native species for hardy subjects in this beautiful group of plants. In sheltered and partially shaded situations, many of the Tree Ferns (fig. 261) may be effectively employed for Summer decoration. Indeed it is probable that in the warm sheltered humid valleys of Southwestern England, Wales, and Ireland, a few of the species from the extreme South of New Zealand and America would flourish with slight protection in very severe weather. The hardiest known are Dickcsonia squarrosa, D. antarctica, Also-pkila Colensoi, Cyathea dealbata and C. medullaris from New Zealand, and Alsophila pruinata from Chili. We append an abbreviated synopsis of the British species, including a few other known hardy species, for which we have adopted what may be termed the Hookerian nomenclature. We have included a few of the more important synonyms, and also the names of the sub-species or varieties commonly seen. But further than this the limits of our work will not permit us to go. The named varieties of British species, distinct or otherwise, offered by Fern-growers, are now numbered by the hundred. Many of them are extremely beautiful, and worthy of cultivation. The species most prolific in varieties are Lomaria Spicant, Asplhium (Athyrium) Filix-foemina, Scolopendrium vnlgare, Polypdium vulgare, and Aspidium (Polystichun) aculeatum,

Fig. 261. Tree Fern.

Fig. 261. Tree Fern.