I. FILICES. 901 



TRIBE VII. OSMUNDE^l. 



Elastic ring embracing a part of the circumference of the sporangium, or 

 reduced to a small disk of cells with thick walls. 



GENERA. 

 Osmunda. Todea. 



TRIBE VIII. MARATTIE^E. 



Sporangia free, appressed, in 2 rows, or in a circle, or confluent, and together 

 resembling a several-celled capsule, deprived of rings, each opening by a slit 

 or pore. 



GENERA. 

 Kaulfussia. Angiopteris. Marattia. Danaea. 



Ferns present such marked characters that in all classifications they form a distinct group. Brong- 

 niart, from whom we have taken most of the details relating to this important family, places near them 

 Marsileacea, Lycopodiacece, Equisetacece and Ckaracece to form his class of Filidnece. He has divided Ferns 

 into several very natural tribes, founded on the structure of the sporangia and their mode of insertion. 



The numerous genera of this vast family have been classed according to the arrangement of the 

 sori and indusia ; but it must be observed that, in certain cases, the sori of the same species appear with 

 and without indusium ; thus Polypodium rugulosum and Hypolepis tenella have been separated, though 

 they are, in fact, the same species j the same may be said of Polystichum venustum and Polypodium 

 sylvaticum, &c. 



' Ferns inhabit the most different climates, from the polar regions ( Woodsia hyperborea, Pteris argcn- 

 tea, &c.), where, however, few species are found, to the tropics, where they are abundant and varied. 

 Many genera are indeed limited to equatorial regions, or extend but little beyond, and then especially in 

 the southern hemisphere. Few genera, on the contrary, are confined to a single continent, and those 

 which are have generally but few species. Most genera have a very wide range, a fact not only true of 

 large genera as limited by Swartz and Willdenow, but generally of those into which they have been 

 subdivided. Some tribes are entirely or almost entirely confined to hot regions ; as Cyatheacece, Cera- 

 topterideee and Hymenophyllece, of which three species only (Trichomanes radicans and Hymenophyllum 

 tunbridf/ense and Wilson?) grow in Europe. All the Tree-ferns, and particularly those of the tribe of 

 Cyatheacece, are tropical, or extend but a little way into some islands situated far from the equator 

 (Ahophila Colcnsoi, Cyathea Smithii, of New Zealand). The arborescent Dicksonia (D. antarctica, Imiata, 

 &c.), extend farther south in New Zealand ; and the Lomarias with an erect but short stem are found in 

 the Magellanic lands. 



' The family of Ferns comprises at least 3,000 described species (the proportion to Phanerogams being 

 as one to thirty), of which about 150 to 200 belong to each of the temperate zones, and 2,600 to the 

 tropical regions of both continents, and to the islands included in this zone. In each of these zones the 

 number of Ferns varies much, according to locality. A peculiar combination of climatic conditions is 

 almost always es&ential to their existence, dry regions producing very few species ; damp, cool and shady 

 places suit them better, and the number of species is so much the greater the more these conditions are 

 fulfilled; insular climates are therefore very favourable to them, and the predominance of Ferns in such 

 has long been noticed. We know, in fact, that the smaller and more distant from continents islands are, 

 the more maritime is their climate, owing to the habitual humidity of the air and its uniform tempera- 

 ture, and the larger is the proportion which Ferns bear to Phsenogamic plants. 



'The family of Ferns, together with Coniferce, has more fossil representatives than any other 



1 These numerical estimates need revision. ED. 



