It IS from the arrangement or difpofition of thefe fced-veffels
that the chara£lcrs of the genera in the proper ferns are at
this time eftabliflied.
^ In tlie genus Ophwglofum, the feed-veifels are placed in Uvo
diftinbl lines, one on each fide of the filament or tongue, giving
it the appearance of a flatted fpike.
In Ofmunda, fome fpecies produce their feed-veffels in
bunches of fliort fpikes at the termination of the fertile leaf,
as in Ofrnund royal, and Moonwort ; in others, they are
arranged in lines along the back of the lobes, as in Curled
Stone Fern, and Rough Spleen wort.
In Acrojlichum, the feed-vellels are difperfed upon and cover
the whole under fide of the lobes.
In Polipodiiim, the fecd-veiTels are difpofed in circular fpots
on the under fide of the lobes.
^ In AJjAenium they are placed in right lines, generally running
in an oblique direaion on the fupine diflc of the leaves
or lobes.
In Ftens, the feed-veffels are placed in lines along the under
margins of the lobes, which are gently rolled backwards.
In Adiantnrn, the feed-veffels are difpofed in ilrort lines, or
oval fpots, near the extremities of the lobes, w'hich are often
terminated by their filmy expanfions that are bent back and
cover them.
In
In Tnchomanes the feed-vefiel is of a globular figure, fingle,
enclofed in its own proper cover, folitary, fupported on its own
filament or footfialk, which arifes from the membranaceous
verge of the rib at the origin of the fécond leaves.
This method of arrangement, though the bcft that has yet
been adopted, is in feveral infiances vague and defe6livc.
In many fpecies of the genus Afplenium, whofe charaacr-
iftic is to have the feed-veffels arranged in difiina lines, they,
Lvhen arrived at maturity, encreafe in breadth fo as to unite
at their extremities and cover the whole under fide of the
lobes; this is frequently the cafe in Afplenium ceterach, Afplenium
ruta-muraria, Afplenium adiantum nigrum, &c. in the
months of September and Oaober.
In feveral of the Polipodia, we obferve the fame confluency
or union in the older ftages of the plants ; fuch for inftance as
Polipodium fragile, Polipodium thelypteris, and Polipodium
fontanum.
In the genus Acroftichum, whofe primary charafter is to
have the under fide of the lobes quite covered with fced-vef-
fels, thefe feed-veffels are difpofed in diftin£I round dots on
the back of the lobes in Acroftichum ilvenfe ; in Acroftichum
feptentrionale they are placed, while immature, in fiiort lines.
The firft of thefe therefore, while young, is a Polipodium,
the laft an Afplenium.
The
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