GENERA OF FERNS. 389 
Dıv. IV. OSMUNDACE®, Mart. 
Sporangia globose, pedicellate, reticulated, unilocular, open- 
ing by a vertical slit (bivalved), apex oblique, gibbous, pellu- 
cid, destitute of an articulated ring. 
Obs. The sporangia being destitute of the radiate apex, 
distinguish this from the preceding division ; but it is to be 
observed that à structure analogous to Schizeacea, is, to a 
certain extent, found in Osmundacee. On examining a spo- 
rangium of this division, a difference is evident in the 
form of the cellular structure on the interior side, indicating 
the line of dehiscence, which line passes over the apparent 
apex of the sporangium, and terminates in a.small indistinct 
_ Striated gibbosity on its exterior side. This:gibbosity must 
be considered as the true apex, which, on account of its 
obliquity, gives the sporangium the appearance of being cleft 
vertically into two equal valves; in that respect forming a 
transition to the following division, Marattiacee, by the 
affinity of Todea with Angiopteris. 
The number of described species constituting Osmunda- 
cee does not exceed twelve; their general habit consists in 
having pinnate or bipinnate fronds, sometimes 6 to 8 feet in 
height, produced from a thick cespitose fleshy rhizoma 
(somewhat analogous to an arborescent rhizoma); the ve- 
nation is free, and the sporangia are borne on separate 
contracted fronds; or in some species, only portions of the 
segments are contracted, and fertile, and, in a few, the sporan- 
gia are definitely produced on the venules of but slightly 
contracted fronds. , 
137. Osmunpba, Linn. 
(Aphyllocarpa, Cav. Plenasium, Presl.) 
Veins forked. Venules direct, free. Fertile fronds, or some 
portion of the segments, contracted, rachiform, simple or 
. compound, densely sporangiferous. 
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