436 PHARMACEUTICAL BOTANY 
ferns are concentric in type but differ from the concentric vascular 
bundles of the stems and leaves of some monocotyledons in that 
xylem is innermost and phloem surrounds the xylem. This kind 
of concentric bundle is called a xylocentric bundle. For further 
details on fern structure see Chapter IV. The dried fronds of 
the native Adiantum pedatum and of the European A. Capillus- 
Veneris are used in domestic medicine as a demulcent expectorant 
in the form of syrup or infusion. 
Famity OsmMuNDACE&.—This family is characterized by 
having short sporangia, the annulus of which consists of a group of 
is 5 
Fic, 328.—Cyrtomium falcatum. Under (dorsal) surface of a portion of a sporophyll, 
showing the numerous sori on the pinnae. (Gager.) 
thick walled cells near the apex on either side of the wall of the 
sporangium, the rest of the wall becoming gradually thinner 
walled. The mature sporangium splits open longitudinally. 
- It is represented in North America by the genus Osmunda, three 
species of which, O. regalis, the royal fern, O. cinnamomea, the 
cinnamon fern and O. claytoniana, the interrupted fern, occur 
locally. The rhizomes and stipe bases of the last named have 
frequently been found as substitutes and adulterants of Aspidium. 
ORDER 2.—HybRopTERALES OR WATER FERNS (HETEROSPOROUS) 
FamiLty Satvintace&.—Floating ferns with broad floating 
leaves and submerged dissected leaves which bear fruit bodies 
called sporocarps containing microsporangia and megasporangia. 
The microsporangia contain microspores which give rise to male 
prothallia. The megasporangia contain megaspores which 
