XCIV. FILICES. 553 
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 late 
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, etc., are natural, and readily recognized ; 
but in Polypodium, Aspidium, Cystopteris, etc., 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 examination 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 not uncommon in cultivation, and 
found occasionally wild, are here wholly passed over. 
Fructification in a terminal spike or panicle. The frond either leaf-like, or 
1 bearing a leaf in the lower part. : : : ° 
Fructification in a little cup or involucre at ‘the edge of the frond : - a tac 
Fructification on the back or under side of some or all the fronds . : a |S 
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 . “a 
Spike simple. Leafentire . : : . 1. OPHIOGLOSSUM. 
Spike branched into a panicle. Leaf pinnate ‘ : 2. BotkyCHIUM. 
( Fronds numerous, scarcely 2 inches high, pinnate, with few deeply-lobed 
4%. Segments. Involucre ovate, 2-lobed : 17. HYMENOPHYLIUM. 
) Fronds 6 or 8 inches high, 2 or 3 times eee with crowded segments. Invo- 
lucre cup-shaped . : 16. TRICHOMANES, 
Fronds tufted, of 2 sorts, the ‘central ones erect, “fruiting, the outer ones barren, 
5 usually shorter, with broader lobes . 2 - : ‘“ 4 “ ~ 
Fruiting and barren fronds similar or nearly so 8 
Fronds (stiff) simply pinnate, with entire lobes, the ‘fruiting linear, the parren 
6 lanceolate. . ll. Burcunum. 
‘ Fronds (delicate) much divided, with small, obovate or oblong, toothed lobes 7 
Sori forming a line close to the margin of the frond . . 5. ALLOSORUS. 
Sori oblong, scattered on the surface of the frond . : . 6. GRAMMITIS. 
Fructification concealed by, or intermixed with, chaffy scales or hairs . . 9 
Fructification in lines along the ae oie of thefronds, the indusium a membrane 
8) attachedtothe margin —. 10 
| Fructification in circular, apne ‘or linear sori, on the under surface, “without. 
chaffy scales. : “ ° . . : : : : o 5K 
