_HYMENOPHYLLÀCEÆ_
The filmy ferns are small, delicate plants with membranaceous, finely
dissected fronds from slender, creeping rootstocks. Sporangia sessile on
a bristle-like receptacle. There are about one hundred species, mostly
tropical, only one of which grows as far north as Kentucky.
[Illustration: Filmy Fern _Trichomanes Boschianum_ (From Waters' "Ferns",
Henry Holt & Co.)]