106 FILICES 
these ferns as having a metallic lustre, owing to a carbonaceous powder with 
which they are covered, and he adds that no other plant exhibits this 
phenomenon. This traveller brought away some of the powder from the 
old trunks of the Aspidium and Meniscium. In the time of Linneus four 
species only of tree-ferns were known, but a large number have been 
described by later botanists; and more than 2,500 species of ferns, com- 
prising the arborescent and herbaceous forms, are known to science. The 
tree-ferns greatly resemble palm-trees in appearance, and the stems of both 
are so much alike, that fossil specimens have frequently been described as 
ferns, but which on further investigation have proved to belong to the Palm 
tribe. 
The conditions under which ferns flourish differ somewhat in different 
genera; but heat, moisture, and shade are necessary for the luxuriant 
development of the greater number. They are more numerous in islands 
than on continents, the arborescent species being almost confined to the 
torrid zone: the shrubby species generally also preferring a climate of 
intense heat, and the herbaceous species grow in temperate climes, and are 
found more rarely in the colder eee while the northern part of the 
globe seems quite destitute of any species of this elegant family of plants. 
As regards the ferns of this kingdom, some grow in almost every county ; 
while some, peculiar to mountainous districts, delighting in limestone soils, 
or thriving only on the basaltic trap, are necessarily, local or rare. Very 
few of our native species will bear the sea-air, yet this is needed for the 
luxuriance of that beautiful plant of the sea-caves and cliffs, the Sea Spleen- 
wort ; while the Wall Rue and Black Spleenwort grace the ruined building 
or barren rock. The Northern Hard Fern is unhurt by its exposure to the 
sun and wind of the heath; and the Lastrea thelypteris is a true marsh fern. 
Most of our ferns luxuriate in a shady spot, on a vegetable mould formed of 
the fallen leaves of many winters, or they wave unseen over the stones of 
quarries, or among rocks; but their number has doubtless been greatly 
lessened by the increase of agriculture during past centuries. 
The terms employed in the description of ferns are few. A linear leaf, 
or leaflet, is one of which the two sides are parallel, like the leaf of the grass : 
the term decurrent signifies that the leafy portion runs down the side of the 
stalk, and gradually merges into it. The margin is sometimes serrated or 
notched like the edge of a saw ; a fertile frond is one bearing the fructifica- 
tion ; a barren frond, one from which that fructification is absent. In some 
ferns, as in the Northern Hard Fern, the barren and fertile fronds are 
differently formed. 
TABLE OF THE ORDERS AND GENERA OF THE BRITISH 
FERNS. 
This order consists of flowerless leafy plants, their leaves or fronds, with 
some few exceptions, gradually unfolding in a scroll-like manner, and bearing 
their spores in capsules on the backs or margins of the fronds. These cap- 
sules are either one-celled and stalked, with an elastic ring; or are without 
stalk or ring. 
