Introduction. 
xiii 
Genus 16. Ceterach. — Sori linear. Indusium very narrow, erect. Frond covered on 
the back with chaffy scales. 
Tribe 6. Scolopendriccc. — Sori as in the Asplenieae, except that the indusia are arranged in 
pairs, and open towards each other. 
Genus 17. Scolopendrium. 
Tribe 7. Aspuhecz. — Sori dorsal, round or nearly so. Indusium superior, attached by its 
centre or an indentation. 
Genus 18. Aspidium. 
** Without an indusium ( Exinvolucratce ). (Tribes 8 and 9.) 
Tribe 8. Polypodiece. — Sori dorsal, round or nearly so. 
Genus 19. Polypodium. 
Tribe 9. Grammitidece. — Sori dorsal, linear or long-oblong. 
Genus 20. Nothochlcena. — Fronds very densely clothed with paleae beneath. 
Genus 21. Gymnogramma. — Fronds without paleae. 
[Tribe Acrosticheoe. — Sori not confined to the veins, but spread over the under-surface (or 
both surfaces) of the frond. No European genus.] 
Sub-Order III. OSMUND ACE.L. — Sporangia stalked, furnished with a short horizontal bar or 
very incomplete ring, splitting vertically. 
Genus 22. Osmunda. 
[Sub-Order Schizccacccc. — Sporangia sessile, crowned by a small, complete, opercular ring, splitting 
vertically. No European genus.] 
[Sub-Order Marattiacece. — Sporangia without a ring, opening by a pore at the apex, and usually 
fused together into a concrete mass. Vernation circinate. No European genus.] 
Sub-Order IV. OpiiioglossacE/E. — S porangia without a ring, opening down the side nearly to 
the base. Vernation erect, not circinate. 
Genus 23. Ophioglossinn. — Sporangia in two rows, connate, two-valved, forming a 
distichous spike. 
Genus 24. Botrychium. — Sporangia separate, two-valved, forming a branched panicle. 
GEOGRAPHICAL DISTRIBUTION OF FERNS. 
Ferns are generally distributed over the globe, being least frequent in the polar regions, 
and most abundant in the tropics, where they attain their most magnificent proportions 
and fullest development in the form of the tree-ferns, which are confined to those regions, or 
extend but slightly beyond them, as in the case of a few species of Cyathea, Dicksonia, and 
Alsophila, which occur in the Cape and New Zealand. Mr. Baker has treated the subject at 
length in the twenty-sixth volume of the “ Transactions of the Linnean Society,” and his paper, 
to which we acknowledge our obligations, should be consulted by those who wish to obtain 
a more complete view of the matter than can be attempted in a sketch like the present. 
He says that here, if anywhere, we may hope to find a large order, with distinctly marked 
and clearly definable climatic relations. “ Without a single prominent exception, we find 
that the whole order, of between two and three thousand clearly marked species, requires 
shade and a damp atmosphere, that everywhere within the tropics there are no ferns at all 
(or very few) in the dry countries and provinces, that, with the precision of an hygrometer, 
an increase in the fern vegetation (it may be in species, or it may be in the number and 
luxuriance of individuals, but usually in both) marks the wooded humid regions, and that, 
d 4 
