. Our native ferns and their allies : with synoptical descriptions of the American Pteridophyta north of Mexico. Ferns. Fig. 3. , Fig. 4. Fig. 5. Fig. 3.—Enlarged sessile sporangium of Trichomanes radicam, Swz. (Original.) Fig. 4.—Sporangium of Scihzsea puisilla, Pursh, showing the apical ring. Much en- larged. (Original.) Fig. 5.—Sporangium of Osmunda regalis, L., showing the rudimentary ring. En- larged. (Original.) 37. In the other sub-orders of Filices the sporangia are variously arranged. In the Hymenophyllace^ or filmy ferns the flattened sporangia are sessile along a filiform receptacle
. Our native ferns and their allies : with synoptical descriptions of the American Pteridophyta north of Mexico. Ferns. Fig. 3. , Fig. 4. Fig. 5. Fig. 3.—Enlarged sessile sporangium of Trichomanes radicam, Swz. (Original.) Fig. 4.—Sporangium of Scihzsea puisilla, Pursh, showing the apical ring. Much en- larged. (Original.) Fig. 5.—Sporangium of Osmunda regalis, L., showing the rudimentary ring. En- larged. (Original.) 37. In the other sub-orders of Filices the sporangia are variously arranged. In the Hymenophyllace^ or filmy ferns the flattened sporangia are sessile along a filiform receptacle and are surrounded with a complete transverse annulus. At maturity they open vertically. (Fig. 3). In the Schiz^ace^ the sporangia are ovate, surrounded at the apex by a complete annulus, and open by a longitudinal slit. (Fig. 4). In the Osmundace^ or flowering ferns the sporangia are larger, globose and naked, with the mere trace of a transverse annulus, and open longitudinally. (Fig. 5). The various methods of fructification can be best understood by describing the peculiarities of the various genera in regular succession and noting the variations occurring in the sections or sub-genera. By this means we will arrive at a better understand- ing of the principles of fern classification as discussed in a future chapter. As the subject of venation is closely connected with that of fructification, it will be treated in the same connection. 38. Acrostichum.—In this genus the sporangia are spread in a stratum over the under surface of the upper pinnae in our soli- tary species, but in some exotics they cover portions of the upper surface as well. There is no indusium. 39. Polypodium.—(Fig. i). This genus contains the largest number of existing ferns, and though all the species agree in the roundish naked sori, the venation is widely different in the various sections which are chiefly formed on the character of the veins. Four of the five sections are represented in our ni
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