XCIV. FILICES. 555 



and almost dust-like, arranged either in clusters, called sort, on 

 the under surface of the frond, and often covered, when young, 

 with a thin membrane, called the indusium, or in little invo- 

 lucres on the margin of the frond ; sometimes rather larger, in 

 spikes or panicles at the top of the frond, which has, lower 

 down, either leafy branches or one leaf. These capsules open 

 in various ways to discharge the minute, usually microscopical 

 spores. 



A very large Order, abundantly diffused over the whole surface of the 

 globe, especially in moist climates, although some species may be found 

 in the chinks of the hottest rocks. The elegance of their foliage has of 

 rate years attracted as much interest in them, on the part of cultivators 

 and amateurs, as has their fructification and germination on the part of 

 the physiologist. It has long been known that they can be reproduced 

 from their spores, but it has only lately been ascertained that these 

 spores when sown develop minute, green, leafy expansions, called 

 prothalli. On the prothallus are produced minute bodies, which have 

 been compared to stamens and pistils, from whence the young Fern is 

 subsequently developed. 



The limitation of genera and species in the Ferns has always been a 

 matter of great difficulty, and of late years their splitting and changing 

 has been carried to such a degree as to throw the whole nomenclature into 

 a state of utter confusion. The best characters are taken from the form 

 and arrangement of the sori and of their indusium ; and some large 

 genera, such as Adiantum, Asplenium, &c, are natural, and readily 

 recognised ; but in Polyjoodium, Aspidium, Cystopteris, &c, there is 

 nothing in habit to serve as a guide, and the indusium of the two latter 

 genera is often so evanescent that it requires the most careful examina- 

 tion of specimens, in exactly the proper state, to ascertain its existence. 

 I have been induced, therefore, with a view to assist the beginner in 

 the determination of the British species, to include in the following- 

 Table of Genera the species also of the most difficult ones, endeavouring 

 to lead to them by more prominent characters, without reference to the 

 more minute, although essential ones, which distinguish the genera. 

 It must be recollected, however, that to determine Ferns they must be 

 in fruit. It is hopeless to attempt to find out by books to what species 

 a barren frond belongs ; and monstrous developments, and deformed 

 fronds, now common in cultivation, and found occasionally wild, are 

 here wholly passed over. 



f Fructification in a terminal, spike or panicle. The frond either leaf -like, or 



.. J bearing a leaf in the lower part 2 



I Fructification in a little cup or involucre at the edge of the frond . . .4 

 ^ Fructification on the back or under side of some or all the fronds . . .5 

 ( Fronds twice pinnate, usually 2 or more feet high, the fructification forming a 



2 < panicle at their extremity 3. Osmunda. 



( Fronds stem-like, not 6 inches high, with a terminal spike or panicle . . 3 



o/ Spike simple. Leaf entire 1. Ophioglossum. 



\ Spike branched into a panicle. Leaf pinnate . . . 2. Botrychium. 

 /"Fronds numerous, scarcely 2 inches high, pinnate, with few deeply-lobed seg- 



4 J ments. Involucre ovate, 2-lobed .... 17. Hymenophyllum. 

 ] Fronds 6 or 8 inches high, 2 or 3 times pinnate, with crowded segments. Invo- 

 t lucre cup-shaped 16. Trichomanes. 



