360 VASCULAR CRYPTOGAMS. 



which is surrounded by a cup-shaped indusium. The antheridia and archegonia are 

 formed for the most part on the surface of the prothallium, and chiefly from its marginal 

 cells. The archegonia are borne on a cushion formed of several layers of cells. The 

 mesophyll of the leaves usually consists of a single layer of cells, and is then necessarily 

 destitute of stomata, which do however occur in Loxsoma on the leaf, which then 

 consists of several layers. The stem is generally creeping and mostly very slender, and 

 furnished with an axial fibro-vascular bundle. True roots are not present in all the 

 species where they are absent, the stem itself is clothed with root-hairs : a large number 

 of species of Trichomanes are described by Mettenius as rootless, and in these cases 

 the ramifications of the stem assume a deceptive root-like appearance. The develop- 

 ment of the axes precedes by a long space that of the leaves; several internodes have 

 usually completely ended their growth while the leaves belonging to them are still very 

 small; and these apparently (or actually?) leafless shoots often branch further to a 

 great extent. The formation of the tissue of these families shows also many pecu- 

 liarities, concerning which reference must be made to Mettenius (Hymenophyllaceae, 

 /. f .). The fertile end of the veins of the leaf projecting beyond its margin, or the colu- 

 mella, elongates by intercalary growth, and the newly formed sporangia are, in a corre- 

 sponding manner, produced in basipetal succession. They are arranged in a spiral line 

 on the columella. The sessile sporangia are biconvex, and are attached to the colu- 

 mella by one of their convex surfaces. The annulus projecting in the form of a cushion 

 which separates the two convexities is usually oblique, and divides the circumference 

 into two unequal portions. In Loxsoma the sporangia are pear-shaped and distinctly 

 stalked. Paraphyses occur only in a few species of Hymenophyllum. 



2. The GleicheniaceaD have sessile sporangia with a complete transverse annulus, 

 and hence a longitudinal dehiscence. The sori are dorsal, without indusium, and mostly 

 formed of a few, sometimes of only three or four, sporangia. The innovation of the 

 lamina of the leaf has already been mentioned. The leaf-stalk is not articulated. 



3. SchizasacesB. The ovoid or pear-shaped sporangia are sessile or shortly stalked; 

 the annulus forms an apical cap-like zone, and is complete and circular, and the 

 dehiscence is therefore longitudinal. The leaf-stalk of all the species contains only one 

 fibro-vascular bundle. In Lygodium the climbing leaf-stalk is indefinite in its growth ; 

 its primary branches end in a lamina which is not circinate, and in L. tenue is trans- 

 formed into a leaf-stalk with indefinite growth. The two pinnae at the base of each 

 primary branch of the leaf have a flatly expanded lamina definite in its growth. The 

 fertile segments are spicate, and each bears on its under side two rows of sporangia, 

 each of which is placed in a pocket-shaped outgrowth of the tissue of the leaf. To 

 this order belong also Schizaea and Aneimia. 



4. Osmundaceae. The sporangia are shortly stalked, unsymmetrically rounded, and 

 furnished on one side, instead of the annulus, with a pecuharly developed group of cells 

 beneath the apex; on the other side they split longitudinally. In Osmunda the fertile 

 leaves or leaf-stalks are contracted, that is, their mesophyll is not developed ; in Todea 

 they resemble the sterile ones. 



5. Cyatheacese. The sporangia have a complete, oblique, eccentric annulus, and 

 transverse dehiscence; the indusia are variable or absent; the sorus generally on a 

 strongly developed receptacle. The leaf-stalk is usually not articulated, passing gradu- 

 ally into the stem. The genera Alsophila, Hemitelia, and Cyathea, include species with 

 columnar stem (Tree-ferns), and large, often compoundly pinnate, leaves. 



6. Polypodiacese. The sporangia have a vertical (/. e. longitudinal) incomplete 

 annulus, and therefore split transversely. Mettenius distinguishes five sub-divisions of 

 this family, which contains the largest number of species of any: — 



