1. _Hymenophyllaceæ._—The Filmy and Bristle Ferns. This family includes some of the simplest kinds of Ferns. There are only three representatives in the United Kingdom. These are _Hymenophyllum tunbridgense_, _H. Wilsoni_, and _Trichomanes radicans_. The two former species are fairly common on rocks which are splashed with water, but the latter seems only to occur in restricted districts in the South of Ireland. All the species must have an abundance of water, or the foliage quickly shrivels. This is due to the fact that the leaves consist of a single layer of cells and are, of course, very thin. A distinctive feature in this family is the bearing of the sporangia; these are almost or entirely stalkless. The sorus, as the group of sporangia is called, is surrounded by an enclosure from the leaf margin. In _Trichomanes_ this is cup-shaped, whilst in _Hymenophyllum_ it is bivalved. The popular name Filmy Fern—bestowed on the Hymenophyllums and allied species—has reference to the semi-transparent nature of the fronds. In the case of _Trichomanes_ the axis on which the sporangia are inserted often projects beyond the cup in which they are contained. This gives a curious spiky appearance to the fertile frond, and hence the name Bristle Fern. 2. _Polypodiaceæ._—This is a very large family, containing two or three times as many species as all the rest of the Vascular Cryptogams put together. Nearly all our native species, with a few exceptions, belong to the family. A distinctive feature is the incomplete annulus of the sporangium. Another point to notice is that the spore cases are stalked. So large is the family that it has been divided into a number of sub-families; the members of these are chiefly characterized by the position of the sorus, the cluster of sporangia on the back of the frond. The different sub-families may be briefly outlined. (_a_) _Davalliaceæ._—There are no British representatives of this family. In this case the sorus is always near to the margin of the leaf, and the indusium or covering is cup-shaped. A familiar species is _Davallia bullata_ from the East; the rhizomes of this Fern are trained into various shapes by the Japanese. (_b_) _Pterideæ._—The Bracken Fern (_Pteris aquilina_), the Maiden Hair (_Adiantum capillus-veneris_), and the Parsley Fern (_Cryptogramme crispus_) belong to this sub-family. A notable feature of the Bracken is the continuous marginal sorus. There is no proper indusium, but the leaf margin curls over and protects the sporangia to some extent. (_c_) _Aspidieæ._—The sorus is in the form of a little rounded heap. The indusium, which is usually kidney-shaped, is supported by a central stalk, somewhat after the manner of a nasturtium leaf. The Male Fern (_Nephrodium filix-mas_) belongs to this sub-family, as well as the Bladder Ferns (_Cystopteris_) and the _Woodsias_.