VASCULARIA. 



419 



the stem form a good polishing-powder, like fine tripoli. In their life- 

 history these plants agree essentially with the Ferns. 



Distribution. The Equisetace86 are found in wet places in most parts 

 of the globe. Calamites and other plants referable to this group occur in 

 the Carboniferous and other rocks. 



FILICES. 



Diagnosis. Asexual Generation : Herbs with a subterraneous 

 rhizome, or trees with an unbranched caudex, with well-developed, 

 generally more or less divided or compound leaves, circinate in 

 vernation, and all or part bearing clusters of sporanges (sori) upon 

 the lower surface (fig. 495, a, b, d) or at the margins (</), seated 

 upon branches of the veins. The sori are either naked (b) or 

 covered at first by a variously formed dehiscent or separating mem- 

 branous structure (induswm, d, e) which is continuous with the 

 epidermis of the leaf. The sporangia are metamorphosed hairs, 

 and the leaves which bear them are sometimes also themselves 

 metamorphosed. An apical cell is not always present, but where 

 it occurs it gives off, in the stem, either two or three series, and in 

 the root always three series of segments. The vascular bundles 

 are very strongly developed, and the central xylem, composed 

 chiefly of sealariform, thiekened tracheides, is surrounded by weak 

 phloem. The Sexual Generation, arising from the spores, consists 

 of independently subsisting monoacious prothallia. 



ILLUSTRATIVE GENERA. 



Tribe 1. POLYPODIES. Sporanyes 

 stalked, with a vertical annulus. 



Acrostichum, L. 

 Gymnogramme, Desc. 

 Oeteracli, Adam. 

 Polypodium, L. 

 Adiantuin, L. 

 Pteris, L. 

 Allosorus, Bernh. 

 Blechnum, L. 

 Asplenium, L. 

 Scolopendrium, Smith. 

 Lastrsea, Presl. 

 Aspidium, Swartz. 

 Cystopteris, Bernh. 



Tribe 2. CYATHEJE. Sporanges 

 sessile, 'more or less elevated on a 

 common receptacle; annulus vertical. 



Alsophila, R. Br. 

 Cyathea, Smith. 



Tribe 3. PARKERIE.E. Sporanges 

 thin, with a broad, imperfect, vertical 

 annulus. 



Ceratopteris, Brongn. 



Parkeria, Hook. 



Tribe 4. HYMENOPHYLLE^:. Spo- 

 ranges on an axis produced by the 

 excurrence of a vein beyond the mar- 

 gin of the leaf ; annulus horizontal 

 or oblique. 



Hymenophyllum, Smith. 

 Trichomanes, L. 



Tribe 5. GLEICHENIEJE. Spo- 

 ranges commonly arranged in fours 

 in the dorsal sori, nearly sessile, 

 with a transverse or oblique annulus; 

 bursting vertically on the inside. 



Gleichenia, Smith. 



Mertensia, Wittd. 



2E2 



