Page:Miscellaneousbot02brow.djvu/268

252 sede all changes in nomenclature, may be inferred from the genus Polypodium alone, though reduced nearly one half by its present character, still including 157 species, or upwards of a seventh part of the whole order.

The expediency of subdividing Polypodium, as well as some of the other genera mentioned, especially Acrostichum, is indeed obvious, not merely on account of their great extent, but also from the striking differences in habit existing among the species referred to each.

I have, some time ago, had an opportunity of remarking, that the plants referred to Polypodium, P. ilvense and hyperboreum, form a distinct genus, from the peculiar structure of their involucrum, even the existence of which had escaped preceding observers.

This genus I have named in honour of my friend Mr. Joseph Woods, whose merits as an accurate and skilful English botanist are well known to many of the members of this Society: and the object of the present communication is to illustrate it by some additional observations on its structure, and by a very perfect drawing, for which I am indebted to the friendship of Mr. Francis Bauer.

The character distinguishing Woodsia from all other genera of Ferns hitherto established, consists in its involucrum being inserted under the group of capsules, or, as it is technically called, the sorus, which it completely sur- rounds at the base ; while it is in every stage open at the top, having its margin divided into a number of capillary segments, which from their length and incurvation entirely conceal the young capsules, and in a great measure the full-grown.

That so singular a structure should have been hitherto unnoticed, even though both species of the genus have been described and figured since the publication of Dr. Smith's memoir, is not perhaps to be wondered at: for the membranaceous base of the involucrum is completely concealed by the capsules, and the marginal hairs, which alone are visible, exactly resembling the pubescence of the frond, have been universally confounded with it.