[Illustration: The Rue Spleenwort. _A. Ruta-muraria_ (Top, Lake
Huron--Lower Left, Mt. Toby, Mass.--Lower Right, Vermont) (From Herbarium
of Geo. E. Davenport)]

This tiny fern grows from small fissures in the limestone cliffs, and
is rather rare in this country; but in Great Britain it is very common,
growing everywhere on walls and ruins. From Mt. Toby, Mass., and Willoughby
Mountain, Vt., to Michigan, Missouri, Kentucky and southward.


B. THE LARGE SPLEENWORTS. _Athýrium_

The following species, which are often two to three feet high and grow in
rich soil, are quite different in appearance and habits from the small rock
spleenworts just described. Some botanists have kept them in the genus
_Asplenium_ because their sori are usually rather straight or only slightly
curved, but others are inclined to follow the practice of the British
botanists and put them into a separate group under _Athýrium_. Nearly all
agree that the lady fern, with its variously curved sori, should be placed
here, and many others would place the silvery spleenwort in the same genus,
partly because of its frequently doubled sori. In regard to the last member
of the group, the narrow-leaved spleenwort, there is more doubt. The sori
taken separately would place it with the _Aspleniums_, but considering its
size, structure, habits of growth and all, it seems more closely allied to
the two larger ferns than to the little rock species. We shall group the
three together as the large spleenworts, or for the sake of being more
definite adopt Clute's felicitous phrase.